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 $245.30   6.513%   $261.2764   $261.28   $261.30   $261.30  
  Purchase #2 $100.98   5.636%   $106.6712   $106.67   $106.65   $106.70  
  Purchase #3 $175.38   6.717%   $187.1603   $187.16   $187.15   $187.20  
  Purchase #4 $104.49   6.399%   $111.1763   $111.18   $111.20   $111.20  
  Purchase #5 $83.78   6.110%   $88.899   $88.90   $88.90   $88.90  
  Purchase #6 $86.31   13.258%   $97.753   $97.75   $97.75   $97.80  
  Purchase #7 $183.61   7.468%   $197.322   $197.32   $197.30   $197.30  
  7 purchase totals = $979.85       $1,050.2582   $1,050.26   $1,050.25   $1,050.40