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	$63.46	11.223%	$70.5821	$70.58	$70.60	$70.60
Purchase #2	$37.56	13.449%	$42.6114	$42.61	$42.60	$42.60
Purchase #3	$200.59	10.250%	$221.1505	$221.15	$221.15	$221.20
Purchase #4	$48.76	8.749%	$53.026	$53.03	$53.05	$53.00
Purchase #5	$59.35	11.663%	$66.272	$66.27	$66.25	$66.30
Purchase #6	$118.31	5.564%	$124.8928	$124.89	$124.90	$124.90
Purchase #7	$105.36	5.538%	$111.1948	$111.19	$111.20	$111.20
7 purchase totals =	$633.39		$689.7296	$689.72	$689.75	$689.80