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 $63.77   13.659%   $72.4803   $72.48   $72.50   $72.50  
  Purchase #2 $230.82   10.271%   $254.5275   $254.53   $254.55   $254.50  
  Purchase #3 $12.92   10.456%   $14.2709   $14.27   $14.25   $14.30  
  Purchase #4 $23.85   8.865%   $25.9643   $25.96   $25.95   $26.00  
  Purchase #5 $195.36   9.291%   $213.5109   $213.51   $213.50   $213.50  
  Purchase #6 $166.44   4.151%   $173.3489   $173.35   $173.35   $173.30  
  Purchase #7 $165.33   7.195%   $177.2255   $177.23   $177.25   $177.20  
  7 purchase totals = $858.49       $931.3283   $931.33   $931.35   $931.30