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 $202.77   12.257%   $227.6235   $227.62   $227.60   $227.60  
  Purchase #2 $169.29   10.587%   $187.2127   $187.21   $187.20   $187.20  
  Purchase #3 $50.86   11.559%   $56.7389   $56.74   $56.75   $56.70  
  Purchase #4 $89.96   9.359%   $98.3794   $98.38   $98.40   $98.40  
  Purchase #5 $157.49   3.697%   $163.3124   $163.31   $163.30   $163.30  
  Purchase #6 $31.27   5.628%   $33.0299   $33.03   $33.05   $33.00  
  Purchase #7 $185.52   12.107%   $207.9809   $207.98   $208.00   $208.00  
  7 purchase totals = $887.16       $974.2777   $974.27   $974.30   $974.20