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	$91.89	8.437%	$99.6428	$99.64	$99.65	$99.60
Purchase #2	$90.48	9.599%	$99.1652	$99.17	$99.15	$99.20
Purchase #3	$71.60	6.333%	$76.1344	$76.13	$76.15	$76.10
Purchase #4	$133.42	6.482%	$142.0683	$142.07	$142.05	$142.10
Purchase #5	$221.71	9.529%	$242.8367	$242.84	$242.85	$242.80
Purchase #6	$42.41	13.275%	$48.0399	$48.04	$48.05	$48.00
Purchase #7	$36.25	8.622%	$39.3755	$39.38	$39.40	$39.40
7 purchase totals =	$687.76		$747.2628	$747.27	$747.30	$747.20