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 $88.74   8.334%   $96.1356   $96.14   $96.15   $96.10  
  Purchase #2 $110.37   13.813%   $125.6154   $125.62   $125.60   $125.60  
  Purchase #3 $87.37   9.847%   $95.9733   $95.97   $95.95   $96.00  
  Purchase #4 $57.90   3.283%   $59.8009   $59.80   $59.80   $59.80  
  Purchase #5 $52.58   13.389%   $59.6199   $59.62   $59.60   $59.60  
  Purchase #6 $230.51   4.262%   $240.3343   $240.33   $240.35   $240.30  
  Purchase #7 $116.99   10.834%   $129.6647   $129.66   $129.65   $129.70  
  7 purchase totals = $744.46       $807.1441   $807.14   $807.10   $807.10