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 $35.33   3.592%   $36.5991   $36.60   $36.60   $36.60  
  Purchase #2 $225.88   7.482%   $242.7803   $242.78   $242.80   $242.80  
  Purchase #3 $151.96   8.475%   $164.8386   $164.84   $164.85   $164.80  
  Purchase #4 $67.36   5.232%   $70.8843   $70.88   $70.90   $70.90  
  Purchase #5 $210.75   9.849%   $231.5068   $231.51   $231.50   $231.50  
  Purchase #6 $132.75   8.800%   $144.432   $144.43   $144.45   $144.40  
  Purchase #7 $9.60   6.372%   $10.2117   $10.21   $10.20   $10.20  
  7 purchase totals = $833.63       $901.2528   $901.25   $901.30   $901.20