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 $59.35   12.427%   $66.7254   $66.73   $66.75   $66.70  
  Purchase #2 $38.50   8.827%   $41.8984   $41.90   $41.90   $41.90  
  Purchase #3 $74.93   8.441%   $81.2548   $81.25   $81.25   $81.30  
  Purchase #4 $230.34   11.226%   $256.198   $256.20   $256.20   $256.20  
  Purchase #5 $224.37   10.551%   $248.0433   $248.04   $248.05   $248.00  
  Purchase #6 $59.53   6.402%   $63.3411   $63.34   $63.35   $63.30  
  Purchase #7 $65.36   4.697%   $68.43   $68.43   $68.45   $68.40  
  7 purchase totals = $752.38       $825.8910   $825.89   $825.95   $825.80