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 $216.91   8.443%   $235.2237   $235.22   $235.20   $235.20  
  Purchase #2 $52.88   11.227%   $58.8168   $58.82   $58.80   $58.80  
  Purchase #3 $9.50   9.337%   $10.387   $10.39   $10.40   $10.40  
  Purchase #4 $131.94   7.183%   $141.4173   $141.42   $141.40   $141.40  
  Purchase #5 $190.46   4.105%   $198.2784   $198.28   $198.30   $198.30  
  Purchase #6 $231.48   10.380%   $255.5076   $255.51   $255.50   $255.50  
  Purchase #7 $110.56   4.283%   $115.2953   $115.30   $115.30   $115.30  
  7 purchase totals = $943.73       $1,014.9261   $1,014.94   $1,014.90   $1,014.90