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 $72.59   3.376%   $75.0406   $75.04   $75.05   $75.00  
  Purchase #2 $193.41   3.228%   $199.6533   $199.65   $199.65   $199.70  
  Purchase #3 $7.85   4.334%   $8.1902   $8.19   $8.20   $8.20  
  Purchase #4 $127.94   6.608%   $136.3943   $136.39   $136.40   $136.40  
  Purchase #5 $68.49   11.406%   $76.302   $76.30   $76.30   $76.30  
  Purchase #6 $189.74   8.293%   $205.4751   $205.48   $205.50   $205.50  
  Purchase #7 $151.50   5.335%   $159.5825   $159.58   $159.60   $159.60  
  7 purchase totals = $811.52       $860.6380   $860.63   $860.70   $860.70