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	$16.84	9.826%	$18.4947	$18.49	$18.50	$18.50
Purchase #2	$68.79	4.516%	$71.8966	$71.90	$71.90	$71.90
Purchase #3	$112.25	13.771%	$127.7079	$127.71	$127.70	$127.70
Purchase #4	$102.29	10.238%	$112.7625	$112.76	$112.75	$112.80
Purchase #5	$33.92	10.620%	$37.5223	$37.52	$37.50	$37.50
Purchase #6	$21.43	11.563%	$23.908	$23.91	$23.90	$23.90
Purchase #7	$248.46	10.611%	$274.8241	$274.82	$274.80	$274.80
7 purchase totals =	$603.98		$667.1161	$667.11	$667.05	$667.10