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 $64.78   13.610%   $73.5966   $73.60   $73.60   $73.60  
  Purchase #2 $184.68   4.849%   $193.6351   $193.64   $193.65   $193.60  
  Purchase #3 $72.70   4.707%   $76.122   $76.12   $76.10   $76.10  
  Purchase #4 $175.40   7.807%   $189.0935   $189.09   $189.10   $189.10  
  Purchase #5 $31.90   6.612%   $34.0092   $34.01   $34.00   $34.00  
  Purchase #6 $75.59   9.578%   $82.83   $82.83   $82.85   $82.80  
  Purchase #7 $79.46   9.177%   $86.752   $86.75   $86.75   $86.80  
  7 purchase totals = $684.51       $736.0384   $736.04   $736.05   $736.00