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 $57.89   10.210%   $63.8006   $63.80   $63.80   $63.80  
  Purchase #2 $50.61   13.440%   $57.412   $57.41   $57.40   $57.40  
  Purchase #3 $166.91   10.840%   $185.003   $185.00   $185.00   $185.00  
  Purchase #4 $230.49   7.784%   $248.4313   $248.43   $248.45   $248.40  
  Purchase #5 $73.41   12.112%   $82.3014   $82.30   $82.30   $82.30  
  Purchase #6 $162.48   13.547%   $184.4912   $184.49   $184.50   $184.50  
  Purchase #7 $195.87   7.726%   $211.0029   $211.00   $211.00   $211.00  
  7 purchase totals = $937.66       $1,032.4424   $1,032.43   $1,032.45   $1,032.40