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 $68.98   4.457%   $72.0544   $72.05   $72.05   $72.10  
  Purchase #2 $53.29   7.431%   $57.25   $57.25   $57.25   $57.30  
  Purchase #3 $28.98   4.426%   $30.2627   $30.26   $30.25   $30.30  
  Purchase #4 $244.32   9.437%   $267.3765   $267.38   $267.40   $267.40  
  Purchase #5 $223.73   13.739%   $254.4683   $254.47   $254.45   $254.50  
  Purchase #6 $108.77   9.423%   $119.0194   $119.02   $119.00   $119.00  
  Purchase #7 $55.37   13.535%   $62.8643   $62.86   $62.85   $62.90  
  7 purchase totals = $783.44       $863.2956   $863.29   $863.25   $863.50