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 $242.30   4.542%   $253.3053   $253.31   $253.30   $253.30  
  Purchase #2 $91.33   3.239%   $94.2882   $94.29   $94.30   $94.30  
  Purchase #3 $116.26   8.243%   $125.8433   $125.84   $125.85   $125.80  
  Purchase #4 $11.46   3.159%   $11.822   $11.82   $11.80   $11.80  
  Purchase #5 $165.87   8.772%   $180.4201   $180.42   $180.40   $180.40  
  Purchase #6 $64.50   7.310%   $69.215   $69.22   $69.20   $69.20  
  Purchase #7 $23.87   4.753%   $25.0045   $25.00   $25.00   $25.00  
  7 purchase totals = $715.59       $759.8984   $759.90   $759.85   $759.80