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 $229.65   10.796%   $254.443   $254.44   $254.45   $254.40  
  Purchase #2 $164.85   6.629%   $175.7779   $175.78   $175.80   $175.80  
  Purchase #3 $69.98   10.857%   $77.5777   $77.58   $77.60   $77.60  
  Purchase #4 $185.68   13.179%   $210.1508   $210.15   $210.15   $210.20  
  Purchase #5 $246.61   6.387%   $262.361   $262.36   $262.35   $262.40  
  Purchase #6 $93.75   8.204%   $101.4413   $101.44   $101.45   $101.40  
  Purchase #7 $125.59   10.203%   $138.4039   $138.40   $138.40   $138.40  
  7 purchase totals = $1,116.11       $1,220.1556   $1,220.15   $1,220.20   $1,220.20