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 $151.49   11.783%   $169.3401   $169.34   $169.35   $169.30  
  Purchase #2 $211.46   11.639%   $236.0718   $236.07   $236.05   $236.10  
  Purchase #3 $9.79   8.309%   $10.6035   $10.60   $10.60   $10.60  
  Purchase #4 $60.34   6.554%   $64.2947   $64.29   $64.30   $64.30  
  Purchase #5 $13.35   8.609%   $14.4993   $14.50   $14.50   $14.50  
  Purchase #6 $160.87   13.347%   $182.3413   $182.34   $182.35   $182.30  
  Purchase #7 $14.88   3.492%   $15.3996   $15.40   $15.40   $15.40  
  7 purchase totals = $622.18       $692.5503   $692.54   $692.55   $692.50