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 $208.25   10.588%   $230.2995   $230.30   $230.30   $230.30  
  Purchase #2 $58.77   11.842%   $65.7295   $65.73   $65.75   $65.70  
  Purchase #3 $156.44   5.427%   $164.93   $164.93   $164.95   $164.90  
  Purchase #4 $152.85   7.345%   $164.0768   $164.08   $164.10   $164.10  
  Purchase #5 $61.77   7.348%   $66.3089   $66.31   $66.30   $66.30  
  Purchase #6 $217.97   4.563%   $227.916   $227.92   $227.90   $227.90  
  Purchase #7 $22.82   5.319%   $24.0338   $24.03   $24.05   $24.00  
  7 purchase totals = $878.87       $943.2945   $943.30   $943.35   $943.20