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 $188.68   11.218%   $209.8461   $209.85   $209.85   $209.80  
  Purchase #2 $54.74   13.179%   $61.9542   $61.95   $61.95   $62.00  
  Purchase #3 $189.83   5.261%   $199.817   $199.82   $199.80   $199.80  
  Purchase #4 $227.98   11.457%   $254.0997   $254.10   $254.10   $254.10  
  Purchase #5 $187.42   11.119%   $208.2592   $208.26   $208.25   $208.30  
  Purchase #6 $249.77   3.605%   $258.7742   $258.77   $258.75   $258.80  
  Purchase #7 $152.83   9.409%   $167.2098   $167.21   $167.20   $167.20  
  7 purchase totals = $1,251.25       $1,359.9602   $1,359.96   $1,359.90   $1,360.00