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	$114.53	8.407%	$124.1585	$124.16	$124.15	$124.20
Purchase #2	$35.72	4.588%	$37.3588	$37.36	$37.35	$37.40
Purchase #3	$16.60	4.872%	$17.4088	$17.41	$17.40	$17.40
Purchase #4	$112.59	9.397%	$123.1701	$123.17	$123.15	$123.20
Purchase #5	$113.66	5.330%	$119.7181	$119.72	$119.70	$119.70
Purchase #6	$12.59	9.764%	$13.8193	$13.82	$13.80	$13.80
Purchase #7	$143.54	11.146%	$159.539	$159.54	$159.55	$159.50
7 purchase totals =	$549.23		$595.1726	$595.18	$595.10	$595.20