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 $69.30   8.609%   $75.266   $75.27   $75.25   $75.30  
  Purchase #2 $109.60   9.202%   $119.6854   $119.69   $119.70   $119.70  
  Purchase #3 $186.56   4.358%   $194.6903   $194.69   $194.70   $194.70  
  Purchase #4 $82.26   13.246%   $93.1562   $93.16   $93.15   $93.20  
  Purchase #5 $112.78   4.259%   $117.5833   $117.58   $117.60   $117.60  
  Purchase #6 $26.73   4.757%   $28.0015   $28.00   $28.00   $28.00  
  Purchase #7 $141.92   12.260%   $159.3194   $159.32   $159.30   $159.30  
  7 purchase totals = $729.15       $787.7021   $787.71   $787.70   $787.80