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	$229.73	12.872%	$259.3008	$259.30	$259.30	$259.30
Purchase #2	$82.52	3.160%	$85.1276	$85.13	$85.15	$85.10
Purchase #3	$152.57	8.203%	$165.0853	$165.09	$165.10	$165.10
Purchase #4	$7.61	8.141%	$8.2295	$8.23	$8.25	$8.20
Purchase #5	$100.72	11.788%	$112.5929	$112.59	$112.60	$112.60
Purchase #6	$138.46	11.773%	$154.7609	$154.76	$154.75	$154.80
Purchase #7	$35.72	3.620%	$37.0131	$37.01	$37.00	$37.00
7 purchase totals =	$747.33		$822.1101	$822.11	$822.15	$822.10