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 $62.82   6.282%   $66.7664   $66.77   $66.75   $66.80  
  Purchase #2 $30.33   8.287%   $32.8434   $32.84   $32.85   $32.80  
  Purchase #3 $120.43   4.362%   $125.6832   $125.68   $125.70   $125.70  
  Purchase #4 $205.30   4.723%   $214.9963   $215.00   $215.00   $215.00  
  Purchase #5 $82.88   3.861%   $86.08   $86.08   $86.10   $86.10  
  Purchase #6 $102.34   3.694%   $106.1204   $106.12   $106.10   $106.10  
  Purchase #7 $48.83   4.641%   $51.0962   $51.10   $51.10   $51.10  
  7 purchase totals = $652.93       $683.5859   $683.59   $683.60   $683.60