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 $249.53   6.817%   $266.5405   $266.54   $266.55   $266.50  
  Purchase #2 $152.70   9.517%   $167.2325   $167.23   $167.25   $167.20  
  Purchase #3 $55.82   7.512%   $60.0132   $60.01   $60.00   $60.00  
  Purchase #4 $43.26   12.823%   $48.8072   $48.81   $48.80   $48.80  
  Purchase #5 $126.91   12.221%   $142.4197   $142.42   $142.40   $142.40  
  Purchase #6 $114.56   7.251%   $122.8667   $122.87   $122.85   $122.90  
  Purchase #7 $95.81   9.235%   $104.6581   $104.66   $104.65   $104.70  
  7 purchase totals = $838.59       $912.5379   $912.54   $912.50   $912.50