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 $57.62   8.667%   $62.6139   $62.61   $62.60   $62.60  
  Purchase #2 $90.99   5.277%   $95.7915   $95.79   $95.80   $95.80  
  Purchase #3 $99.90   10.668%   $110.5573   $110.56   $110.55   $110.60  
  Purchase #4 $206.46   6.733%   $220.361   $220.36   $220.35   $220.40  
  Purchase #5 $175.69   13.353%   $199.1499   $199.15   $199.15   $199.10  
  Purchase #6 $135.47   11.761%   $151.4026   $151.40   $151.40   $151.40  
  Purchase #7 $60.50   9.831%   $66.4478   $66.45   $66.45   $66.40  
  7 purchase totals = $826.63       $906.3240   $906.32   $906.30   $906.30