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	$48.51	4.109%	$50.5033	$50.50	$50.50	$50.50
Purchase #2	$248.46	6.467%	$264.5279	$264.53	$264.55	$264.50
Purchase #3	$160.73	11.780%	$179.664	$179.66	$179.65	$179.70
Purchase #4	$131.88	10.609%	$145.8711	$145.87	$145.85	$145.90
Purchase #5	$92.53	10.736%	$102.464	$102.46	$102.45	$102.50
Purchase #6	$178.53	5.778%	$188.8455	$188.85	$188.85	$188.80
Purchase #7	$10.72	12.443%	$12.0539	$12.05	$12.05	$12.10
7 purchase totals =	$871.36		$943.9297	$943.92	$943.90	$944.00