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	$45.89	9.175%	$50.1004	$50.10	$50.10	$50.10
Purchase #2	$226.68	6.593%	$241.625	$241.63	$241.65	$241.60
Purchase #3	$123.41	3.583%	$127.8318	$127.83	$127.85	$127.80
Purchase #4	$103.30	11.661%	$115.3458	$115.35	$115.35	$115.30
Purchase #5	$116.54	7.170%	$124.8959	$124.90	$124.90	$124.90
Purchase #6	$243.44	8.202%	$263.4069	$263.41	$263.40	$263.40
Purchase #7	$59.83	12.503%	$67.3105	$67.31	$67.30	$67.30
7 purchase totals =	$919.09		$990.5163	$990.53	$990.55	$990.40