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 $93.83   5.497%   $98.9878   $98.99   $99.00   $99.00  
  Purchase #2 $214.26   7.285%   $229.8688   $229.87   $229.85   $229.90  
  Purchase #3 $90.39   13.236%   $102.354   $102.35   $102.35   $102.40  
  Purchase #4 $86.99   6.798%   $92.9036   $92.90   $92.90   $92.90  
  Purchase #5 $216.96   7.641%   $233.5379   $233.54   $233.55   $233.50  
  Purchase #6 $224.76   9.278%   $245.6132   $245.61   $245.60   $245.60  
  Purchase #7 $32.29   11.596%   $36.0343   $36.03   $36.05   $36.00  
  7 purchase totals = $959.48       $1,039.2996   $1,039.29   $1,039.30   $1,039.30