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 $59.96   13.824%   $68.2489   $68.25   $68.25   $68.20  
  Purchase #2 $169.27   4.767%   $177.3391   $177.34   $177.35   $177.30  
  Purchase #3 $28.78   9.291%   $31.4539   $31.45   $31.45   $31.50  
  Purchase #4 $245.80   6.309%   $261.3075   $261.31   $261.30   $261.30  
  Purchase #5 $85.47   7.135%   $91.5683   $91.57   $91.55   $91.60  
  Purchase #6 $16.93   12.868%   $19.1086   $19.11   $19.10   $19.10  
  Purchase #7 $225.49   13.131%   $255.0991   $255.10   $255.10   $255.10  
  7 purchase totals = $831.70       $904.1254   $904.13   $904.10   $904.10