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	$152.92	11.316%	$170.2244	$170.22	$170.20	$170.20
Purchase #2	$85.68	4.358%	$89.4139	$89.41	$89.40	$89.40
Purchase #3	$80.43	4.823%	$84.3091	$84.31	$84.30	$84.30
Purchase #4	$35.84	12.217%	$40.2186	$40.22	$40.20	$40.20
Purchase #5	$187.59	8.755%	$204.0135	$204.01	$204.00	$204.00
Purchase #6	$127.57	3.144%	$131.5808	$131.58	$131.60	$131.60
Purchase #7	$244.83	4.668%	$256.2587	$256.26	$256.25	$256.30
7 purchase totals =	$914.86		$976.0190	$976.01	$975.95	$976.00