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 $53.57   13.363%   $60.7286   $60.73   $60.75   $60.70  
  Purchase #2 $173.46   5.421%   $182.8633   $182.86   $182.85   $182.90  
  Purchase #3 $29.57   13.245%   $33.4865   $33.49   $33.50   $33.50  
  Purchase #4 $86.67   12.534%   $97.5332   $97.53   $97.55   $97.50  
  Purchase #5 $142.59   8.329%   $154.4663   $154.47   $154.45   $154.50  
  Purchase #6 $124.94   4.247%   $130.2462   $130.25   $130.25   $130.20  
  Purchase #7 $197.80   5.733%   $209.1399   $209.14   $209.15   $209.10  
  7 purchase totals = $808.60       $868.4640   $868.47   $868.50   $868.40