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	$166.39	10.447%	$183.7728	$183.77	$183.75	$183.80
Purchase #2	$17.29	5.621%	$18.2619	$18.26	$18.25	$18.30
Purchase #3	$98.55	8.466%	$106.8932	$106.89	$106.90	$106.90
Purchase #4	$54.46	9.103%	$59.4175	$59.42	$59.40	$59.40
Purchase #5	$84.71	6.524%	$90.2365	$90.24	$90.25	$90.20
Purchase #6	$57.44	8.581%	$62.3689	$62.37	$62.35	$62.40
Purchase #7	$35.64	13.126%	$40.3181	$40.32	$40.30	$40.30
7 purchase totals =	$514.48		$561.2689	$561.27	$561.20	$561.30