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 $60.33   6.598%   $64.3106   $64.31   $64.30   $64.30  
  Purchase #2 $178.47   9.257%   $194.991   $194.99   $195.00   $195.00  
  Purchase #3 $20.74   6.162%   $22.018   $22.02   $22.00   $22.00  
  Purchase #4 $151.94   3.768%   $157.6651   $157.67   $157.65   $157.70  
  Purchase #5 $142.49   7.637%   $153.372   $153.37   $153.35   $153.40  
  Purchase #6 $164.94   11.856%   $184.4953   $184.50   $184.50   $184.50  
  Purchase #7 $248.89   6.528%   $265.1375   $265.14   $265.15   $265.10  
  7 purchase totals = $967.80       $1,041.9895   $1,042.00   $1,041.95   $1,042.00