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	$52.72	11.589%	$58.8297	$58.83	$58.85	$58.80
Purchase #2	$11.62	5.152%	$12.2187	$12.22	$12.20	$12.20
Purchase #3	$220.30	4.359%	$229.9029	$229.90	$229.90	$229.90
Purchase #4	$151.69	6.342%	$161.3102	$161.31	$161.30	$161.30
Purchase #5	$97.92	6.144%	$103.9362	$103.94	$103.95	$103.90
Purchase #6	$41.40	13.373%	$46.9364	$46.94	$46.95	$46.90
Purchase #7	$80.90	11.413%	$90.1331	$90.13	$90.15	$90.10
7 purchase totals =	$656.55		$703.2672	$703.27	$703.30	$703.10