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 $236.99   8.260%   $256.5654   $256.57   $256.55   $256.60  
  Purchase #2 $180.73   8.317%   $195.7613   $195.76   $195.75   $195.80  
  Purchase #3 $61.51   4.843%   $64.4889   $64.49   $64.50   $64.50  
  Purchase #4 $181.67   8.511%   $197.1319   $197.13   $197.15   $197.10  
  Purchase #5 $80.79   12.403%   $90.8104   $90.81   $90.80   $90.80  
  Purchase #6 $215.43   10.113%   $237.2164   $237.22   $237.20   $237.20  
  Purchase #7 $148.28   7.655%   $159.6308   $159.63   $159.65   $159.60  
  7 purchase totals = $1,105.40       $1,201.6051   $1,201.61   $1,201.60   $1,201.60