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	$74.64	5.733%	$78.9191	$78.92	$78.90	$78.90
Purchase #2	$63.98	6.476%	$68.1233	$68.12	$68.10	$68.10
Purchase #3	$25.62	3.780%	$26.5884	$26.59	$26.60	$26.60
Purchase #4	$143.40	5.140%	$150.7708	$150.77	$150.75	$150.80
Purchase #5	$146.39	3.333%	$151.2692	$151.27	$151.25	$151.30
Purchase #6	$36.62	5.428%	$38.6077	$38.61	$38.60	$38.60
Purchase #7	$38.64	8.863%	$42.0647	$42.06	$42.05	$42.10
7 purchase totals =	$529.29		$556.3432	$556.34	$556.25	$556.40