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 $232.96   13.357%   $264.0765   $264.08   $264.10   $264.10  
  Purchase #2 $97.63   7.397%   $104.8517   $104.85   $104.85   $104.90  
  Purchase #3 $17.70   11.193%   $19.6812   $19.68   $19.70   $19.70  
  Purchase #4 $20.58   13.857%   $23.4318   $23.43   $23.45   $23.40  
  Purchase #5 $203.50   8.730%   $221.2656   $221.27   $221.25   $221.30  
  Purchase #6 $135.49   3.702%   $140.5058   $140.51   $140.50   $140.50  
  Purchase #7 $20.98   3.311%   $21.6746   $21.67   $21.65   $21.70  
  7 purchase totals = $728.84       $795.4872   $795.49   $795.50   $795.60