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	$59.36	6.588%	$63.2706	$63.27	$63.25	$63.30
Purchase #2	$42.92	6.691%	$45.7918	$45.79	$45.80	$45.80
Purchase #3	$159.75	8.596%	$173.4821	$173.48	$173.50	$173.50
Purchase #4	$166.50	5.831%	$176.2086	$176.21	$176.20	$176.20
Purchase #5	$214.37	3.813%	$222.5439	$222.54	$222.55	$222.50
Purchase #6	$36.53	11.144%	$40.6009	$40.60	$40.60	$40.60
Purchase #7	$175.61	11.690%	$196.1388	$196.14	$196.15	$196.10
7 purchase totals =	$855.04		$918.0367	$918.03	$918.05	$918.00