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	$26.53	7.406%	$28.4948	$28.49	$28.50	$28.50
Purchase #2	$54.29	5.810%	$57.4442	$57.44	$57.45	$57.40
Purchase #3	$5.94	5.775%	$6.283	$6.28	$6.30	$6.30
Purchase #4	$198.41	4.417%	$207.1738	$207.17	$207.15	$207.20
Purchase #5	$90.84	10.456%	$100.3382	$100.34	$100.35	$100.30
Purchase #6	$181.40	13.136%	$205.2287	$205.23	$205.25	$205.20
Purchase #7	$91.69	9.583%	$100.4767	$100.48	$100.50	$100.50
7 purchase totals =	$649.10		$705.4394	$705.43	$705.50	$705.40