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	$222.91	13.860%	$253.8053	$253.81	$253.80	$253.80
Purchase #2	$31.29	12.608%	$35.235	$35.24	$35.25	$35.20
Purchase #3	$235.80	12.150%	$264.4497	$264.45	$264.45	$264.40
Purchase #4	$159.87	7.694%	$172.1704	$172.17	$172.15	$172.20
Purchase #5	$123.93	3.133%	$127.8127	$127.81	$127.80	$127.80
Purchase #6	$212.69	5.512%	$224.4135	$224.41	$224.40	$224.40
Purchase #7	$232.72	8.719%	$253.0109	$253.01	$253.00	$253.00
7 purchase totals =	$1,219.21		$1,330.8975	$1,330.90	$1,330.85	$1,330.80