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	$245.73	12.252%	$275.8368	$275.84	$275.85	$275.80
Purchase #2	$130.51	6.160%	$138.5494	$138.55	$138.55	$138.50
Purchase #3	$168.51	3.450%	$174.3236	$174.32	$174.30	$174.30
Purchase #4	$83.94	9.777%	$92.1468	$92.15	$92.15	$92.10
Purchase #5	$80.52	11.839%	$90.0528	$90.05	$90.05	$90.10
Purchase #6	$119.66	6.314%	$127.2153	$127.22	$127.20	$127.20
Purchase #7	$208.81	11.176%	$232.1466	$232.15	$232.15	$232.10
7 purchase totals =	$1,037.68		$1,130.2713	$1,130.28	$1,130.25	$1,130.10