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	$130.60	13.253%	$147.9084	$147.91	$147.90	$147.90
Purchase #2	$98.37	13.596%	$111.7444	$111.74	$111.75	$111.70
Purchase #3	$79.45	12.547%	$89.4186	$89.42	$89.40	$89.40
Purchase #4	$172.94	8.396%	$187.46	$187.46	$187.45	$187.50
Purchase #5	$106.73	11.408%	$118.9058	$118.91	$118.90	$118.90
Purchase #6	$233.46	4.584%	$244.1618	$244.16	$244.15	$244.20
Purchase #7	$69.39	3.214%	$71.6202	$71.62	$71.60	$71.60
7 purchase totals =	$890.94		$971.2192	$971.22	$971.15	$971.20