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	$143.58	6.159%	$152.4231	$152.42	$152.40	$152.40
Purchase #2	$101.43	9.475%	$111.0405	$111.04	$111.05	$111.00
Purchase #3	$112.52	13.298%	$127.4829	$127.48	$127.50	$127.50
Purchase #4	$166.68	8.254%	$180.4378	$180.44	$180.45	$180.40
Purchase #5	$95.48	11.575%	$106.5318	$106.53	$106.55	$106.50
Purchase #6	$77.29	11.414%	$86.1119	$86.11	$86.10	$86.10
Purchase #7	$142.69	3.375%	$147.5058	$147.51	$147.50	$147.50
7 purchase totals =	$839.67		$911.5338	$911.53	$911.55	$911.40