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 $60.71   6.681%   $64.766   $64.77   $64.75   $64.80  
  Purchase #2 $94.56   11.857%   $105.772   $105.77   $105.75   $105.80  
  Purchase #3 $86.38   6.562%   $92.0483   $92.05   $92.05   $92.00  
  Purchase #4 $147.52   13.821%   $167.9087   $167.91   $167.90   $167.90  
  Purchase #5 $111.70   6.704%   $119.1884   $119.19   $119.20   $119.20  
  Purchase #6 $187.74   11.545%   $209.4146   $209.41   $209.40   $209.40  
  Purchase #7 $19.36   6.350%   $20.5894   $20.59   $20.60   $20.60  
  7 purchase totals = $707.97       $779.6874   $779.69   $779.65   $779.70