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 $63.62   13.684%   $72.3258   $72.33   $72.35   $72.30  
  Purchase #2 $132.98   10.659%   $147.1543   $147.15   $147.15   $147.20  
  Purchase #3 $76.31   5.775%   $80.7169   $80.72   $80.70   $80.70  
  Purchase #4 $23.94   9.170%   $26.1353   $26.14   $26.15   $26.10  
  Purchase #5 $61.73   5.546%   $65.1535   $65.15   $65.15   $65.20  
  Purchase #6 $218.61   10.429%   $241.4088   $241.41   $241.40   $241.40  
  Purchase #7 $190.94   4.352%   $199.2497   $199.25   $199.25   $199.20  
  7 purchase totals = $768.13       $832.1443   $832.15   $832.15   $832.10