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	$220.51	8.213%	$238.6205	$238.62	$238.60	$238.60
Purchase #2	$63.61	11.867%	$71.1586	$71.16	$71.15	$71.20
Purchase #3	$199.26	6.251%	$211.7157	$211.72	$211.70	$211.70
Purchase #4	$39.62	3.201%	$40.8882	$40.89	$40.90	$40.90
Purchase #5	$61.25	3.581%	$63.4434	$63.44	$63.45	$63.40
Purchase #6	$150.59	9.513%	$164.9156	$164.92	$164.90	$164.90
Purchase #7	$55.35	10.305%	$61.0538	$61.05	$61.05	$61.10
7 purchase totals =	$790.19		$851.7958	$851.80	$851.75	$851.80