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	$211.51	8.327%	$229.1224	$229.12	$229.10	$229.10
Purchase #2	$212.69	3.337%	$219.7875	$219.79	$219.80	$219.80
Purchase #3	$91.47	9.117%	$99.8093	$99.81	$99.80	$99.80
Purchase #4	$123.35	3.465%	$127.6241	$127.62	$127.60	$127.60
Purchase #5	$70.71	4.500%	$73.892	$73.89	$73.90	$73.90
Purchase #6	$63.71	4.520%	$66.5897	$66.59	$66.60	$66.60
Purchase #7	$18.85	7.813%	$20.3228	$20.32	$20.30	$20.30
7 purchase totals =	$792.29		$837.1478	$837.14	$837.10	$837.10