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	$6.63	10.624%	$7.3344	$7.33	$7.35	$7.30
Purchase #2	$174.72	3.355%	$180.5819	$180.58	$180.60	$180.60
Purchase #3	$173.37	13.431%	$196.6553	$196.66	$196.65	$196.70
Purchase #4	$162.50	3.514%	$168.2103	$168.21	$168.20	$168.20
Purchase #5	$140.73	13.695%	$160.003	$160.00	$160.00	$160.00
Purchase #6	$230.61	3.798%	$239.3686	$239.37	$239.35	$239.40
Purchase #7	$169.91	10.287%	$187.3886	$187.39	$187.40	$187.40
7 purchase totals =	$1,058.47		$1,139.5421	$1,139.54	$1,139.55	$1,139.60