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 $59.88   8.760%   $65.1255   $65.13   $65.15   $65.10  
  Purchase #2 $214.29   11.606%   $239.1605   $239.16   $239.15   $239.20  
  Purchase #3 $15.94   4.748%   $16.6968   $16.70   $16.70   $16.70  
  Purchase #4 $96.75   6.771%   $103.3009   $103.30   $103.30   $103.30  
  Purchase #5 $10.39   6.538%   $11.0693   $11.07   $11.05   $11.10  
  Purchase #6 $40.49   3.159%   $41.7691   $41.77   $41.75   $41.80  
  Purchase #7 $89.30   8.355%   $96.761   $96.76   $96.75   $96.80  
  7 purchase totals = $527.04       $573.8831   $573.89   $573.85   $574.00