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	$24.71	13.300%	$27.9964	$28.00	$28.00	$28.00
Purchase #2	$11.91	8.392%	$12.9095	$12.91	$12.90	$12.90
Purchase #3	$172.86	8.366%	$187.3215	$187.32	$187.30	$187.30
Purchase #4	$30.83	11.608%	$34.4087	$34.41	$34.40	$34.40
Purchase #5	$23.63	11.622%	$26.3763	$26.38	$26.40	$26.40
Purchase #6	$53.25	11.468%	$59.3567	$59.36	$59.35	$59.40
Purchase #7	$72.73	13.748%	$82.7289	$82.73	$82.75	$82.70
7 purchase totals =	$389.92		$431.0980	$431.11	$431.10	$431.10