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	$60.52	13.539%	$68.7138	$68.71	$68.70	$68.70
Purchase #2	$39.59	8.407%	$42.9183	$42.92	$42.90	$42.90
Purchase #3	$58.50	6.141%	$62.0925	$62.09	$62.10	$62.10
Purchase #4	$141.41	6.849%	$151.0952	$151.10	$151.10	$151.10
Purchase #5	$31.69	12.455%	$35.637	$35.64	$35.65	$35.60
Purchase #6	$19.52	7.168%	$20.9192	$20.92	$20.90	$20.90
Purchase #7	$23.87	5.430%	$25.1661	$25.17	$25.15	$25.20
7 purchase totals =	$375.10		$406.5421	$406.55	$406.50	$406.50