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 $113.81   11.442%   $126.8321   $126.83   $126.85   $126.80  
  Purchase #2 $108.31   8.871%   $117.9182   $117.92   $117.90   $117.90  
  Purchase #3 $164.35   3.128%   $169.4909   $169.49   $169.50   $169.50  
  Purchase #4 $27.40   9.751%   $30.0718   $30.07   $30.05   $30.10  
  Purchase #5 $207.47   7.293%   $222.6008   $222.60   $222.60   $222.60  
  Purchase #6 $65.80   5.155%   $69.192   $69.19   $69.20   $69.20  
  Purchase #7 $201.99   8.352%   $218.8602   $218.86   $218.85   $218.90  
  7 purchase totals = $889.13       $954.9660   $954.96   $954.95   $955.00