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	$205.43	11.671%	$229.4057	$229.41	$229.40	$229.40
Purchase #2	$180.71	10.828%	$200.2773	$200.28	$200.30	$200.30
Purchase #3	$127.93	3.465%	$132.3628	$132.36	$132.35	$132.40
Purchase #4	$59.82	12.218%	$67.1288	$67.13	$67.15	$67.10
Purchase #5	$131.30	12.650%	$147.9095	$147.91	$147.90	$147.90
Purchase #6	$240.25	5.489%	$253.4373	$253.44	$253.45	$253.40
Purchase #7	$48.78	3.418%	$50.4473	$50.45	$50.45	$50.40
7 purchase totals =	$994.22		$1,080.9687	$1,080.98	$1,081.00	$1,080.90