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	$73.40	6.758%	$78.3604	$78.36	$78.35	$78.40
Purchase #2	$36.51	5.315%	$38.4505	$38.45	$38.45	$38.50
Purchase #3	$130.93	11.763%	$146.3313	$146.33	$146.35	$146.30
Purchase #4	$51.44	12.143%	$57.6864	$57.69	$57.70	$57.70
Purchase #5	$6.89	4.245%	$7.1825	$7.18	$7.20	$7.20
Purchase #6	$11.70	11.278%	$13.0195	$13.02	$13.00	$13.00
Purchase #7	$168.25	12.766%	$189.7288	$189.73	$189.75	$189.70
7 purchase totals =	$479.12		$530.7594	$530.76	$530.80	$530.80