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 $81.28   13.473%   $92.2309   $92.23   $92.25   $92.20  
  Purchase #2 $75.44   9.492%   $82.6008   $82.60   $82.60   $82.60  
  Purchase #3 $5.75   8.375%   $6.2316   $6.23   $6.25   $6.20  
  Purchase #4 $245.63   5.557%   $259.2797   $259.28   $259.30   $259.30  
  Purchase #5 $90.29   4.839%   $94.6591   $94.66   $94.65   $94.70  
  Purchase #6 $28.66   10.363%   $31.63   $31.63   $31.65   $31.60  
  Purchase #7 $142.27   6.270%   $151.1903   $151.19   $151.20   $151.20  
  7 purchase totals = $669.32       $717.8224   $717.82   $717.90   $717.80