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	$123.93	5.341%	$130.5491	$130.55	$130.55	$130.50
Purchase #2	$53.68	10.262%	$59.1886	$59.19	$59.20	$59.20
Purchase #3	$121.64	3.642%	$126.0701	$126.07	$126.05	$126.10
Purchase #4	$65.87	12.507%	$74.1084	$74.11	$74.10	$74.10
Purchase #5	$29.83	4.397%	$31.1416	$31.14	$31.15	$31.10
Purchase #6	$6.73	8.126%	$7.2769	$7.28	$7.30	$7.30
Purchase #7	$65.65	10.194%	$72.3424	$72.34	$72.35	$72.30
7 purchase totals =	$467.33		$500.6771	$500.68	$500.70	$500.60