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 $10.48   12.212%   $11.7598   $11.76   $11.75   $11.80  
  Purchase #2 $235.85   7.760%   $254.152   $254.15   $254.15   $254.20  
  Purchase #3 $241.28   8.202%   $261.0698   $261.07   $261.05   $261.10  
  Purchase #4 $56.52   7.139%   $60.555   $60.56   $60.55   $60.60  
  Purchase #5 $88.86   13.185%   $100.5762   $100.58   $100.60   $100.60  
  Purchase #6 $27.54   9.578%   $30.1778   $30.18   $30.20   $30.20  
  Purchase #7 $107.96   9.612%   $118.3371   $118.34   $118.35   $118.30  
  7 purchase totals = $768.49       $836.6277   $836.64   $836.65   $836.80