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 $246.78   6.652%   $263.1958   $263.20   $263.20   $263.20  
  Purchase #2 $23.97   5.129%   $25.1994   $25.20   $25.20   $25.20  
  Purchase #3 $113.66   10.487%   $125.5795   $125.58   $125.60   $125.60  
  Purchase #4 $223.81   5.445%   $235.9965   $236.00   $236.00   $236.00  
  Purchase #5 $93.59   9.344%   $102.335   $102.34   $102.35   $102.30  
  Purchase #6 $18.44   7.122%   $19.7533   $19.75   $19.75   $19.80  
  Purchase #7 $164.27   7.411%   $176.444   $176.44   $176.45   $176.40  
  7 purchase totals = $884.52       $948.5035   $948.51   $948.55   $948.50