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 $182.94   11.114%   $203.272   $203.27   $203.25   $203.30  
  Purchase #2 $14.29   9.551%   $15.6548   $15.65   $15.65   $15.70  
  Purchase #3 $11.94   8.814%   $12.9924   $12.99   $13.00   $13.00  
  Purchase #4 $214.39   4.445%   $223.9196   $223.92   $223.90   $223.90  
  Purchase #5 $83.38   9.345%   $91.1719   $91.17   $91.15   $91.20  
  Purchase #6 $151.52   5.131%   $159.2945   $159.29   $159.30   $159.30  
  Purchase #7 $53.81   8.707%   $58.4952   $58.50   $58.50   $58.50  
  7 purchase totals = $712.27       $764.8004   $764.79   $764.75   $764.90