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	$12.25	6.639%	$13.0633	$13.06	$13.05	$13.10
Purchase #2	$56.78	4.350%	$59.2499	$59.25	$59.25	$59.20
Purchase #3	$231.30	5.139%	$243.1865	$243.19	$243.20	$243.20
Purchase #4	$169.61	3.306%	$175.2173	$175.22	$175.20	$175.20
Purchase #5	$204.91	6.683%	$218.6041	$218.60	$218.60	$218.60
Purchase #6	$195.47	11.735%	$218.4084	$218.41	$218.40	$218.40
Purchase #7	$135.84	11.837%	$151.9194	$151.92	$151.90	$151.90
7 purchase totals =	$1,006.16		$1,079.6489	$1,079.65	$1,079.60	$1,079.60