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 $46.95   8.371%   $50.8802   $50.88   $50.90   $50.90  
  Purchase #2 $174.83   11.584%   $195.0823   $195.08   $195.10   $195.10  
  Purchase #3 $74.67   4.164%   $77.7793   $77.78   $77.80   $77.80  
  Purchase #4 $119.48   11.554%   $133.2847   $133.28   $133.30   $133.30  
  Purchase #5 $174.42   10.747%   $193.1649   $193.16   $193.15   $193.20  
  Purchase #6 $115.73   9.433%   $126.6468   $126.65   $126.65   $126.60  
  Purchase #7 $190.98   9.411%   $208.9531   $208.95   $208.95   $209.00  
  7 purchase totals = $897.06       $985.7913   $985.78   $985.85   $985.90