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 $30.44   11.560%   $33.9589   $33.96   $33.95   $34.00  
  Purchase #2 $131.69   7.717%   $141.8525   $141.85   $141.85   $141.90  
  Purchase #3 $169.30   8.622%   $183.897   $183.90   $183.90   $183.90  
  Purchase #4 $210.47   3.271%   $217.3545   $217.35   $217.35   $217.40  
  Purchase #5 $128.83   4.780%   $134.9881   $134.99   $135.00   $135.00  
  Purchase #6 $95.54   12.363%   $107.3516   $107.35   $107.35   $107.40  
  Purchase #7 $187.75   3.266%   $193.8819   $193.88   $193.90   $193.90  
  7 purchase totals = $954.02       $1,013.2845   $1,013.28   $1,013.30   $1,013.50