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 $84.97   9.159%   $92.7524   $92.75   $92.75   $92.80  
  Purchase #2 $26.27   11.644%   $29.3289   $29.33   $29.35   $29.30  
  Purchase #3 $112.95   11.377%   $125.8003   $125.80   $125.80   $125.80  
  Purchase #4 $30.39   11.463%   $33.8736   $33.87   $33.85   $33.90  
  Purchase #5 $100.53   6.247%   $106.8101   $106.81   $106.80   $106.80  
  Purchase #6 $129.98   5.733%   $137.4318   $137.43   $137.45   $137.40  
  Purchase #7 $250.99   10.279%   $276.7893   $276.79   $276.80   $276.80  
  7 purchase totals = $736.08       $802.7864   $802.78   $802.80   $802.80