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 $227.72   5.546%   $240.3494   $240.35   $240.35   $240.30  
  Purchase #2 $64.50   4.352%   $67.307   $67.31   $67.30   $67.30  
  Purchase #3 $59.59   9.391%   $65.1861   $65.19   $65.20   $65.20  
  Purchase #4 $93.89   12.798%   $105.906   $105.91   $105.90   $105.90  
  Purchase #5 $180.34   8.567%   $195.7897   $195.79   $195.80   $195.80  
  Purchase #6 $93.44   4.163%   $97.3299   $97.33   $97.35   $97.30  
  Purchase #7 $66.98   10.201%   $73.8126   $73.81   $73.80   $73.80  
  7 purchase totals = $786.46       $845.6807   $845.69   $845.70   $845.60