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 $78.86   6.201%   $83.7501   $83.75   $83.75   $83.80  
  Purchase #2 $93.67   13.429%   $106.2489   $106.25   $106.25   $106.20  
  Purchase #3 $60.47   11.116%   $67.1918   $67.19   $67.20   $67.20  
  Purchase #4 $82.27   9.743%   $90.2856   $90.29   $90.30   $90.30  
  Purchase #5 $213.91   3.866%   $222.1798   $222.18   $222.20   $222.20  
  Purchase #6 $151.54   12.572%   $170.5916   $170.59   $170.60   $170.60  
  Purchase #7 $204.62   6.403%   $217.7218   $217.72   $217.70   $217.70  
  7 purchase totals = $885.34       $957.9696   $957.97   $958.00   $958.00