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	$120.82	5.316%	$127.2428	$127.24	$127.25	$127.20
Purchase #2	$204.41	12.275%	$229.5013	$229.50	$229.50	$229.50
Purchase #3	$124.42	7.356%	$133.5723	$133.57	$133.55	$133.60
Purchase #4	$117.50	10.114%	$129.384	$129.38	$129.40	$129.40
Purchase #5	$72.82	10.570%	$80.5171	$80.52	$80.50	$80.50
Purchase #6	$91.83	13.145%	$103.9011	$103.90	$103.90	$103.90
Purchase #7	$204.40	4.847%	$214.3073	$214.31	$214.30	$214.30
7 purchase totals =	$936.20		$1,018.4259	$1,018.42	$1,018.40	$1,018.40