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 $213.66   11.509%   $238.2501   $238.25   $238.25   $238.30  
  Purchase #2 $19.34   4.191%   $20.1505   $20.15   $20.15   $20.20  
  Purchase #3 $220.70   8.181%   $238.7555   $238.76   $238.75   $238.80  
  Purchase #4 $109.99   4.183%   $114.5909   $114.59   $114.60   $114.60  
  Purchase #5 $25.42   5.207%   $26.7436   $26.74   $26.75   $26.70  
  Purchase #6 $46.99   7.541%   $50.5335   $50.53   $50.55   $50.50  
  Purchase #7 $59.53   9.122%   $64.9603   $64.96   $64.95   $65.00  
  7 purchase totals = $695.63       $753.9844   $753.98   $754.00   $754.10