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 $41.99   4.762%   $43.9896   $43.99   $44.00   $44.00  
  Purchase #2 $125.97   3.529%   $130.4155   $130.42   $130.40   $130.40  
  Purchase #3 $159.38   13.767%   $181.3218   $181.32   $181.30   $181.30  
  Purchase #4 $96.84   8.691%   $105.2564   $105.26   $105.25   $105.30  
  Purchase #5 $245.27   11.139%   $272.5906   $272.59   $272.60   $272.60  
  Purchase #6 $20.83   5.549%   $21.9859   $21.99   $22.00   $22.00  
  Purchase #7 $138.99   12.464%   $156.3137   $156.31   $156.30   $156.30  
  7 purchase totals = $829.27       $911.8735   $911.88   $911.85   $911.90