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 $42.99   11.831%   $48.0761   $48.08   $48.10   $48.10  
  Purchase #2 $103.74   9.271%   $113.3577   $113.36   $113.35   $113.40  
  Purchase #3 $115.98   3.352%   $119.8676   $119.87   $119.85   $119.90  
  Purchase #4 $180.41   8.355%   $195.4833   $195.48   $195.50   $195.50  
  Purchase #5 $92.85   3.178%   $95.8008   $95.80   $95.80   $95.80  
  Purchase #6 $128.77   13.643%   $146.3381   $146.34   $146.35   $146.30  
  Purchase #7 $12.52   3.601%   $12.9708   $12.97   $12.95   $13.00  
  7 purchase totals = $677.26       $731.8944   $731.90   $731.90   $732.00