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	$222.81	6.421%	$237.1166	$237.12	$237.10	$237.10
Purchase #2	$29.82	11.255%	$33.1762	$33.18	$33.20	$33.20
Purchase #3	$128.82	8.171%	$139.3459	$139.35	$139.35	$139.30
Purchase #4	$71.98	7.645%	$77.4829	$77.48	$77.50	$77.50
Purchase #5	$146.75	3.672%	$152.1387	$152.14	$152.15	$152.10
Purchase #6	$185.65	4.225%	$193.4937	$193.49	$193.50	$193.50
Purchase #7	$153.75	13.752%	$174.8937	$174.89	$174.90	$174.90
7 purchase totals =	$939.58		$1,007.6477	$1,007.65	$1,007.70	$1,007.60