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	$139.31	6.551%	$148.4362	$148.44	$148.45	$148.40
Purchase #2	$180.69	9.314%	$197.5195	$197.52	$197.50	$197.50
Purchase #3	$116.58	9.552%	$127.7157	$127.72	$127.70	$127.70
Purchase #4	$187.25	7.816%	$201.8855	$201.89	$201.90	$201.90
Purchase #5	$54.37	10.541%	$60.1011	$60.10	$60.10	$60.10
Purchase #6	$97.50	5.485%	$102.8479	$102.85	$102.85	$102.80
Purchase #7	$153.58	7.464%	$165.0432	$165.04	$165.05	$165.00
7 purchase totals =	$929.28		$1,003.5491	$1,003.56	$1,003.55	$1,003.40