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 $238.98   3.418%   $247.1483   $247.15   $247.15   $247.10  
  Purchase #2 $26.41   8.121%   $28.5548   $28.55   $28.55   $28.60  
  Purchase #3 $19.39   7.632%   $20.8698   $20.87   $20.85   $20.90  
  Purchase #4 $69.97   8.570%   $75.9664   $75.97   $75.95   $76.00  
  Purchase #5 $222.80   5.865%   $235.8672   $235.87   $235.85   $235.90  
  Purchase #6 $89.40   9.804%   $98.1648   $98.16   $98.15   $98.20  
  Purchase #7 $53.25   13.302%   $60.3333   $60.33   $60.35   $60.30  
  7 purchase totals = $720.20       $766.9046   $766.90   $766.85   $767.00