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 $41.48   11.503%   $46.2514   $46.25   $46.25   $46.30  
  Purchase #2 $229.99   7.591%   $247.4485   $247.45   $247.45   $247.40  
  Purchase #3 $174.50   4.857%   $182.9755   $182.98   $183.00   $183.00  
  Purchase #4 $128.88   6.626%   $137.4196   $137.42   $137.40   $137.40  
  Purchase #5 $110.54   11.568%   $123.3273   $123.33   $123.35   $123.30  
  Purchase #6 $19.73   4.116%   $20.5421   $20.54   $20.55   $20.50  
  Purchase #7 $117.50   7.103%   $125.846   $125.85   $125.85   $125.80  
  7 purchase totals = $822.62       $883.8104   $883.82   $883.85   $883.70