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 $216.77   4.214%   $225.9047   $225.90   $225.90   $225.90  
  Purchase #2 $93.67   11.196%   $104.1573   $104.16   $104.15   $104.20  
  Purchase #3 $139.58   8.133%   $150.932   $150.93   $150.95   $150.90  
  Purchase #4 $220.29   13.609%   $250.2693   $250.27   $250.25   $250.30  
  Purchase #5 $139.30   10.325%   $153.6827   $153.68   $153.70   $153.70  
  Purchase #6 $20.69   10.202%   $22.8008   $22.80   $22.80   $22.80  
  Purchase #7 $32.33   12.634%   $36.4146   $36.41   $36.40   $36.40  
  7 purchase totals = $862.63       $944.1614   $944.15   $944.15   $944.20