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	$20.78	6.494%	$22.1295	$22.13	$22.15	$22.10
Purchase #2	$219.42	8.623%	$238.3406	$238.34	$238.35	$238.30
Purchase #3	$37.38	7.473%	$40.1734	$40.17	$40.15	$40.20
Purchase #4	$99.35	12.795%	$112.0618	$112.06	$112.05	$112.10
Purchase #5	$89.87	6.695%	$95.8868	$95.89	$95.90	$95.90
Purchase #6	$164.34	4.337%	$171.4674	$171.47	$171.45	$171.50
Purchase #7	$32.31	10.400%	$35.6702	$35.67	$35.65	$35.70
7 purchase totals =	$663.45		$715.7297	$715.73	$715.70	$715.80