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 $67.33   13.372%   $76.3334   $76.33   $76.35   $76.30  
  Purchase #2 $7.96   13.656%   $9.047   $9.05   $9.05   $9.00  
  Purchase #3 $50.97   13.810%   $58.009   $58.01   $58.00   $58.00  
  Purchase #4 $87.87   12.422%   $98.7852   $98.79   $98.80   $98.80  
  Purchase #5 $238.83   4.190%   $248.837   $248.84   $248.85   $248.80  
  Purchase #6 $23.75   5.393%   $25.0308   $25.03   $25.05   $25.00  
  Purchase #7 $125.71   8.296%   $136.1389   $136.14   $136.15   $136.10  
  7 purchase totals = $602.42       $652.1813   $652.19   $652.25   $652.00