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	$175.50	10.264%	$193.5133	$193.51	$193.50	$193.50
Purchase #2	$89.36	11.162%	$99.3344	$99.33	$99.35	$99.30
Purchase #3	$68.53	3.840%	$71.1616	$71.16	$71.15	$71.20
Purchase #4	$67.95	4.662%	$71.1178	$71.12	$71.10	$71.10
Purchase #5	$40.27	8.296%	$43.6108	$43.61	$43.60	$43.60
Purchase #6	$18.65	13.288%	$21.1282	$21.13	$21.15	$21.10
Purchase #7	$8.56	12.575%	$9.6364	$9.64	$9.65	$9.60
7 purchase totals =	$468.82		$509.5025	$509.50	$509.50	$509.40