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 $142.74   8.116%   $154.3248   $154.32   $154.30   $154.30  
  Purchase #2 $244.83   9.192%   $267.3348   $267.33   $267.35   $267.30  
  Purchase #3 $153.63   7.551%   $165.2306   $165.23   $165.25   $165.20  
  Purchase #4 $200.95   11.363%   $223.7839   $223.78   $223.80   $223.80  
  Purchase #5 $143.60   12.822%   $162.0124   $162.01   $162.00   $162.00  
  Purchase #6 $216.86   8.720%   $235.7702   $235.77   $235.75   $235.80  
  Purchase #7 $115.38   10.785%   $127.8237   $127.82   $127.80   $127.80  
  7 purchase totals = $1,217.99       $1,336.2804   $1,336.26   $1,336.25   $1,336.20