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 $105.74   13.113%   $119.6057   $119.61   $119.60   $119.60  
  Purchase #2 $23.56   8.429%   $25.5459   $25.55   $25.55   $25.50  
  Purchase #3 $87.61   3.775%   $90.9173   $90.92   $90.90   $90.90  
  Purchase #4 $141.28   11.799%   $157.9496   $157.95   $157.95   $157.90  
  Purchase #5 $192.76   5.537%   $203.4331   $203.43   $203.45   $203.40  
  Purchase #6 $205.45   7.624%   $221.1135   $221.11   $221.10   $221.10  
  Purchase #7 $118.83   11.214%   $132.1556   $132.16   $132.15   $132.20  
  7 purchase totals = $875.23       $950.7207   $950.73   $950.70   $950.60