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 $202.83   6.362%   $215.734   $215.73   $215.75   $215.70  
  Purchase #2 $161.44   11.695%   $180.3204   $180.32   $180.30   $180.30  
  Purchase #3 $73.63   13.202%   $83.3506   $83.35   $83.35   $83.40  
  Purchase #4 $207.95   13.206%   $235.4119   $235.41   $235.40   $235.40  
  Purchase #5 $87.28   7.634%   $93.943   $93.94   $93.95   $93.90  
  Purchase #6 $28.88   10.822%   $32.0054   $32.01   $32.00   $32.00  
  Purchase #7 $72.70   3.553%   $75.283   $75.28   $75.30   $75.30  
  7 purchase totals = $834.71       $916.0483   $916.04   $916.05   $916.00