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	$80.78	11.316%	$89.9211	$89.92	$89.90	$89.90
Purchase #2	$61.92	8.522%	$67.1968	$67.20	$67.20	$67.20
Purchase #3	$30.54	8.767%	$33.2174	$33.22	$33.20	$33.20
Purchase #4	$28.84	12.185%	$32.3542	$32.35	$32.35	$32.40
Purchase #5	$195.52	8.251%	$211.6524	$211.65	$211.65	$211.70
Purchase #6	$85.92	5.221%	$90.4059	$90.41	$90.40	$90.40
Purchase #7	$18.31	8.629%	$19.89	$19.89	$19.90	$19.90
7 purchase totals =	$501.83		$544.6378	$544.64	$544.60	$544.70