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 $60.97   3.563%   $63.1424   $63.14   $63.15   $63.10  
  Purchase #2 $19.92   4.720%   $20.8602   $20.86   $20.85   $20.90  
  Purchase #3 $17.69   8.862%   $19.2577   $19.26   $19.25   $19.30  
  Purchase #4 $55.98   9.485%   $61.2897   $61.29   $61.30   $61.30  
  Purchase #5 $146.78   8.558%   $159.3414   $159.34   $159.35   $159.30  
  Purchase #6 $90.28   4.784%   $94.599   $94.60   $94.60   $94.60  
  Purchase #7 $71.37   4.369%   $74.4882   $74.49   $74.50   $74.50  
  7 purchase totals = $462.99       $492.9786   $492.98   $493.00   $493.00