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	$102.74	8.284%	$111.251	$111.25	$111.25	$111.30
Purchase #2	$135.46	11.337%	$150.8171	$150.82	$150.80	$150.80
Purchase #3	$39.65	13.854%	$45.1431	$45.14	$45.15	$45.10
Purchase #4	$181.73	9.222%	$198.4891	$198.49	$198.50	$198.50
Purchase #5	$229.95	7.688%	$247.6286	$247.63	$247.65	$247.60
Purchase #6	$16.67	9.716%	$18.2897	$18.29	$18.30	$18.30
Purchase #7	$179.88	3.118%	$185.4887	$185.49	$185.50	$185.50
7 purchase totals =	$886.08		$957.1073	$957.11	$957.15	$957.10