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	$143.50	11.258%	$159.6552	$159.66	$159.65	$159.70
Purchase #2	$130.57	12.763%	$147.2346	$147.23	$147.25	$147.20
Purchase #3	$198.46	7.715%	$213.7712	$213.77	$213.75	$213.80
Purchase #4	$75.42	7.679%	$81.2115	$81.21	$81.20	$81.20
Purchase #5	$204.86	11.539%	$228.4988	$228.50	$228.50	$228.50
Purchase #6	$112.41	13.676%	$127.7832	$127.78	$127.80	$127.80
Purchase #7	$222.81	4.715%	$233.3155	$233.32	$233.30	$233.30
7 purchase totals =	$1,088.03		$1,191.4700	$1,191.47	$1,191.45	$1,191.50