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 $88.41   4.104%   $92.0383   $92.04   $92.05   $92.00  
  Purchase #2 $152.40   5.531%   $160.8292   $160.83   $160.85   $160.80  
  Purchase #3 $60.54   6.773%   $64.6404   $64.64   $64.65   $64.60  
  Purchase #4 $224.97   10.591%   $248.7966   $248.80   $248.80   $248.80  
  Purchase #5 $223.74   6.333%   $237.9095   $237.91   $237.90   $237.90  
  Purchase #6 $228.68   13.114%   $258.6691   $258.67   $258.65   $258.70  
  Purchase #7 $227.29   13.810%   $258.6787   $258.68   $258.70   $258.70  
  7 purchase totals = $1,206.03       $1,321.5618   $1,321.57   $1,321.60   $1,321.50