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 $191.92   5.222%   $201.9421   $201.94   $201.95   $201.90  
  Purchase #2 $116.57   8.489%   $126.4656   $126.47   $126.45   $126.50  
  Purchase #3 $209.87   8.788%   $228.3134   $228.31   $228.30   $228.30  
  Purchase #4 $46.51   11.791%   $51.994   $51.99   $52.00   $52.00  
  Purchase #5 $43.78   13.229%   $49.5717   $49.57   $49.55   $49.60  
  Purchase #6 $240.28   6.330%   $255.4897   $255.49   $255.50   $255.50  
  Purchase #7 $30.75   5.264%   $32.3687   $32.37   $32.35   $32.40  
  7 purchase totals = $879.68       $946.1452   $946.14   $946.10   $946.20