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 $171.52   13.490%   $194.658   $194.66   $194.65   $194.70  
  Purchase #2 $14.26   9.183%   $15.5695   $15.57   $15.55   $15.60  
  Purchase #3 $169.84   4.847%   $178.0721   $178.07   $178.05   $178.10  
  Purchase #4 $101.47   3.517%   $105.0387   $105.04   $105.05   $105.00  
  Purchase #5 $216.94   5.693%   $229.2904   $229.29   $229.30   $229.30  
  Purchase #6 $82.87   5.322%   $87.2803   $87.28   $87.30   $87.30  
  Purchase #7 $143.79   3.269%   $148.4905   $148.49   $148.50   $148.50  
  7 purchase totals = $900.69       $958.3995   $958.40   $958.40   $958.50