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	$231.34	9.428%	$253.1507	$253.15	$253.15	$253.20
Purchase #2	$98.77	11.709%	$110.335	$110.34	$110.35	$110.30
Purchase #3	$234.36	10.628%	$259.2678	$259.27	$259.25	$259.30
Purchase #4	$87.52	3.629%	$90.6961	$90.70	$90.70	$90.70
Purchase #5	$212.79	4.483%	$222.3294	$222.33	$222.35	$222.30
Purchase #6	$61.60	6.308%	$65.4857	$65.49	$65.50	$65.50
Purchase #7	$139.33	3.646%	$144.41	$144.41	$144.40	$144.40
7 purchase totals =	$1,065.71		$1,145.6747	$1,145.69	$1,145.70	$1,145.70