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 $60.57   12.261%   $67.9965   $68.00   $68.00   $68.00  
  Purchase #2 $234.88   3.170%   $242.3257   $242.33   $242.35   $242.30  
  Purchase #3 $139.85   11.374%   $155.7565   $155.76   $155.75   $155.80  
  Purchase #4 $129.59   5.848%   $137.1684   $137.17   $137.15   $137.20  
  Purchase #5 $237.31   5.190%   $249.6264   $249.63   $249.65   $249.60  
  Purchase #6 $137.51   3.567%   $142.415   $142.42   $142.40   $142.40  
  Purchase #7 $231.78   12.137%   $259.9111   $259.91   $259.90   $259.90  
  7 purchase totals = $1,171.49       $1,255.1996   $1,255.22   $1,255.20   $1,255.20