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 $212.63   11.818%   $237.7586   $237.76   $237.75   $237.80  
  Purchase #2 $56.79   9.786%   $62.3475   $62.35   $62.35   $62.30  
  Purchase #3 $117.70   11.771%   $131.5545   $131.55   $131.55   $131.60  
  Purchase #4 $46.63   8.616%   $50.6476   $50.65   $50.65   $50.60  
  Purchase #5 $142.35   8.415%   $154.3288   $154.33   $154.35   $154.30  
  Purchase #6 $67.76   12.446%   $76.1934   $76.19   $76.20   $76.20  
  Purchase #7 $230.47   5.853%   $243.9594   $243.96   $243.95   $244.00  
  7 purchase totals = $874.33       $956.7898   $956.79   $956.80   $956.80