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 $133.72   4.619%   $139.8965   $139.90   $139.90   $139.90  
  Purchase #2 $62.86   3.399%   $64.9966   $65.00   $65.00   $65.00  
  Purchase #3 $202.99   5.501%   $214.1565   $214.16   $214.15   $214.20  
  Purchase #4 $182.41   8.261%   $197.4789   $197.48   $197.50   $197.50  
  Purchase #5 $114.88   4.714%   $120.2954   $120.30   $120.30   $120.30  
  Purchase #6 $193.28   4.504%   $201.9853   $201.99   $202.00   $202.00  
  Purchase #7 $217.37   7.437%   $233.5358   $233.54   $233.55   $233.50  
  7 purchase totals = $1,107.51       $1,172.3450   $1,172.37   $1,172.40   $1,172.40