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 $58.86   8.302%   $63.7466   $63.75   $63.75   $63.70  
  Purchase #2 $124.92   7.679%   $134.5126   $134.51   $134.50   $134.50  
  Purchase #3 $203.92   7.232%   $218.6675   $218.67   $218.65   $218.70  
  Purchase #4 $248.63   9.647%   $272.6153   $272.62   $272.60   $272.60  
  Purchase #5 $234.43   7.239%   $251.4004   $251.40   $251.40   $251.40  
  Purchase #6 $229.25   13.566%   $260.3501   $260.35   $260.35   $260.40  
  Purchase #7 $131.56   11.177%   $146.2645   $146.26   $146.25   $146.30  
  7 purchase totals = $1,231.57       $1,347.5570   $1,347.56   $1,347.50   $1,347.60