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 $64.84   12.675%   $73.0585   $73.06   $73.05   $73.10  
  Purchase #2 $103.79   3.290%   $107.2047   $107.20   $107.20   $107.20  
  Purchase #3 $107.89   10.804%   $119.5464   $119.55   $119.55   $119.50  
  Purchase #4 $99.34   6.352%   $105.6501   $105.65   $105.65   $105.70  
  Purchase #5 $58.32   5.489%   $61.5212   $61.52   $61.50   $61.50  
  Purchase #6 $107.36   7.327%   $115.2263   $115.23   $115.25   $115.20  
  Purchase #7 $31.48   3.105%   $32.4575   $32.46   $32.45   $32.50  
  7 purchase totals = $573.02       $614.6647   $614.67   $614.65   $614.70