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 $49.77   8.274%   $53.888   $53.89   $53.90   $53.90  
  Purchase #2 $83.88   13.859%   $95.5049   $95.50   $95.50   $95.50  
  Purchase #3 $91.44   13.626%   $103.8996   $103.90   $103.90   $103.90  
  Purchase #4 $24.87   8.829%   $27.0658   $27.07   $27.05   $27.10  
  Purchase #5 $206.65   10.191%   $227.7097   $227.71   $227.70   $227.70  
  Purchase #6 $159.25   7.237%   $170.7749   $170.77   $170.75   $170.80  
  Purchase #7 $236.71   13.146%   $267.8279   $267.83   $267.85   $267.80  
  7 purchase totals = $852.57       $946.6708   $946.67   $946.65   $946.70