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 $240.84   9.209%   $263.019   $263.02   $263.00   $263.00  
  Purchase #2 $83.61   4.620%   $87.4728   $87.47   $87.45   $87.50  
  Purchase #3 $166.37   13.516%   $188.8566   $188.86   $188.85   $188.90  
  Purchase #4 $208.72   5.449%   $220.0932   $220.09   $220.10   $220.10  
  Purchase #5 $12.27   11.595%   $13.6927   $13.69   $13.70   $13.70  
  Purchase #6 $248.86   3.265%   $256.9853   $256.99   $257.00   $257.00  
  Purchase #7 $71.74   9.211%   $78.348   $78.35   $78.35   $78.30  
  7 purchase totals = $1,032.41       $1,108.4676   $1,108.47   $1,108.45   $1,108.50