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	$74.90	3.502%	$77.523	$77.52	$77.50	$77.50
Purchase #2	$39.43	6.684%	$42.0655	$42.07	$42.05	$42.10
Purchase #3	$138.90	12.475%	$156.2278	$156.23	$156.25	$156.20
Purchase #4	$147.36	11.483%	$164.2813	$164.28	$164.30	$164.30
Purchase #5	$32.76	8.622%	$35.5846	$35.58	$35.60	$35.60
Purchase #6	$160.83	11.832%	$179.8594	$179.86	$179.85	$179.90
Purchase #7	$99.59	4.763%	$104.3335	$104.33	$104.35	$104.30
7 purchase totals =	$693.77		$759.8751	$759.87	$759.90	$759.90