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 $241.33   8.136%   $260.9646   $260.96   $260.95   $261.00  
  Purchase #2 $67.26   8.181%   $72.7625   $72.76   $72.75   $72.80  
  Purchase #3 $32.63   8.521%   $35.4104   $35.41   $35.40   $35.40  
  Purchase #4 $126.98   5.648%   $134.1518   $134.15   $134.15   $134.20  
  Purchase #5 $184.25   8.660%   $200.2061   $200.21   $200.20   $200.20  
  Purchase #6 $227.51   7.629%   $244.8667   $244.87   $244.85   $244.90  
  Purchase #7 $124.50   5.638%   $131.5193   $131.52   $131.50   $131.50  
  7 purchase totals = $1,004.46       $1,079.8814   $1,079.88   $1,079.80   $1,080.00