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 $86.49   9.206%   $94.4523   $94.45   $94.45   $94.50  
  Purchase #2 $64.97   5.151%   $68.3166   $68.32   $68.30   $68.30  
  Purchase #3 $68.49   13.213%   $77.5396   $77.54   $77.55   $77.50  
  Purchase #4 $210.73   3.678%   $218.4806   $218.48   $218.50   $218.50  
  Purchase #5 $32.74   11.340%   $36.4527   $36.45   $36.45   $36.50  
  Purchase #6 $81.35   6.119%   $86.3278   $86.33   $86.35   $86.30  
  Purchase #7 $217.93   13.201%   $246.6989   $246.70   $246.70   $246.70  
  7 purchase totals = $762.70       $828.2685   $828.27   $828.30   $828.30