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 $48.66   11.336%   $54.1761   $54.18   $54.20   $54.20  
  Purchase #2 $103.78   12.157%   $116.3965   $116.40   $116.40   $116.40  
  Purchase #3 $114.37   11.308%   $127.303   $127.30   $127.30   $127.30  
  Purchase #4 $94.85   3.468%   $98.1394   $98.14   $98.15   $98.10  
  Purchase #5 $21.93   4.843%   $22.9921   $22.99   $23.00   $23.00  
  Purchase #6 $15.74   11.871%   $17.6085   $17.61   $17.60   $17.60  
  Purchase #7 $134.95   10.621%   $149.283   $149.28   $149.30   $149.30  
  7 purchase totals = $534.28       $585.8986   $585.90   $585.95   $585.90