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 $58.56   12.433%   $65.8408   $65.84   $65.85   $65.80  
  Purchase #2 $92.99   13.128%   $105.1977   $105.20   $105.20   $105.20  
  Purchase #3 $139.68   13.474%   $158.5005   $158.50   $158.50   $158.50  
  Purchase #4 $173.61   12.266%   $194.905   $194.91   $194.90   $194.90  
  Purchase #5 $8.52   4.221%   $8.8796   $8.88   $8.90   $8.90  
  Purchase #6 $87.91   4.318%   $91.706   $91.71   $91.70   $91.70  
  Purchase #7 $250.95   3.371%   $259.4095   $259.41   $259.40   $259.40  
  7 purchase totals = $812.22       $884.4391   $884.45   $884.45   $884.40