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	$75.90	9.642%	$83.2183	$83.22	$83.20	$83.20
Purchase #2	$97.83	6.325%	$104.0177	$104.02	$104.00	$104.00
Purchase #3	$147.27	12.244%	$165.3017	$165.30	$165.30	$165.30
Purchase #4	$140.51	11.159%	$156.1895	$156.19	$156.20	$156.20
Purchase #5	$35.42	5.109%	$37.2296	$37.23	$37.25	$37.20
Purchase #6	$84.86	11.620%	$94.7207	$94.72	$94.70	$94.70
Purchase #7	$7.39	7.198%	$7.9219	$7.92	$7.90	$7.90
7 purchase totals =	$589.18		$648.5994	$648.60	$648.55	$648.50