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 $72.87   5.257%   $76.7008   $76.70   $76.70   $76.70  
  Purchase #2 $46.80   10.323%   $51.6312   $51.63   $51.65   $51.60  
  Purchase #3 $197.90   9.526%   $216.752   $216.75   $216.75   $216.80  
  Purchase #4 $158.57   9.308%   $173.3297   $173.33   $173.35   $173.30  
  Purchase #5 $167.50   7.850%   $180.6488   $180.65   $180.65   $180.60  
  Purchase #6 $250.73   8.327%   $271.6083   $271.61   $271.60   $271.60  
  Purchase #7 $10.90   13.162%   $12.3347   $12.33   $12.35   $12.30  
  7 purchase totals = $905.27       $983.0055   $983.00   $983.05   $982.90