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 $237.61   11.743%   $265.5125   $265.51   $265.50   $265.50  
  Purchase #2 $70.95   7.533%   $76.2947   $76.29   $76.30   $76.30  
  Purchase #3 $185.78   5.258%   $195.5483   $195.55   $195.55   $195.50  
  Purchase #4 $144.96   12.810%   $163.5294   $163.53   $163.55   $163.50  
  Purchase #5 $86.35   11.487%   $96.269   $96.27   $96.25   $96.30  
  Purchase #6 $57.25   13.126%   $64.7646   $64.76   $64.75   $64.80  
  Purchase #7 $105.95   13.732%   $120.4991   $120.50   $120.50   $120.50  
  7 purchase totals = $888.85       $982.4176   $982.41   $982.40   $982.40