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	$11.41	13.241%	$12.9208	$12.92	$12.90	$12.90
Purchase #2	$232.70	12.430%	$261.6246	$261.62	$261.60	$261.60
Purchase #3	$170.58	3.130%	$175.9192	$175.92	$175.90	$175.90
Purchase #4	$41.95	4.142%	$43.6876	$43.69	$43.70	$43.70
Purchase #5	$122.77	3.459%	$127.0166	$127.02	$127.00	$127.00
Purchase #6	$42.84	13.474%	$48.6123	$48.61	$48.60	$48.60
Purchase #7	$90.52	6.588%	$96.4835	$96.48	$96.50	$96.50
7 purchase totals =	$712.77		$766.2646	$766.26	$766.20	$766.20