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	$119.56	6.795%	$127.6841	$127.68	$127.70	$127.70
Purchase #2	$99.99	11.546%	$111.5348	$111.53	$111.55	$111.50
Purchase #3	$176.92	9.532%	$193.784	$193.78	$193.80	$193.80
Purchase #4	$90.44	7.274%	$97.0186	$97.02	$97.00	$97.00
Purchase #5	$115.74	13.623%	$131.5073	$131.51	$131.50	$131.50
Purchase #6	$94.86	7.851%	$102.3075	$102.31	$102.30	$102.30
Purchase #7	$37.34	13.394%	$42.3413	$42.34	$42.35	$42.30
7 purchase totals =	$734.85		$806.1776	$806.17	$806.20	$806.10