Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $212.64   7.586%   $228.7709   $228.77   $228.75   $228.80  
  Purchase #2 $221.95   10.144%   $244.4646   $244.46   $244.45   $244.50  
  Purchase #3 $235.59   5.347%   $248.187   $248.19   $248.20   $248.20  
  Purchase #4 $119.25   12.174%   $133.7675   $133.77   $133.75   $133.80  
  Purchase #5 $214.91   11.555%   $239.7429   $239.74   $239.75   $239.70  
  Purchase #6 $208.75   13.210%   $236.3259   $236.33   $236.35   $236.30  
  Purchase #7 $244.90   7.652%   $263.6397   $263.64   $263.65   $263.60  
  7 purchase totals = $1,457.99       $1,594.8985   $1,594.90   $1,594.90   $1,594.90