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 $98.54   3.817%   $102.3013   $102.30   $102.30   $102.30  
  Purchase #2 $63.87   3.512%   $66.1131   $66.11   $66.10   $66.10  
  Purchase #3 $204.51   11.782%   $228.6054   $228.61   $228.60   $228.60  
  Purchase #4 $107.69   11.128%   $119.6737   $119.67   $119.65   $119.70  
  Purchase #5 $69.49   8.300%   $75.2577   $75.26   $75.25   $75.30  
  Purchase #6 $105.79   11.251%   $117.6924   $117.69   $117.70   $117.70  
  Purchase #7 $213.30   13.867%   $242.8783   $242.88   $242.90   $242.90  
  7 purchase totals = $863.19       $952.5219   $952.52   $952.50   $952.60