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	$94.81	4.545%	$99.1191	$99.12	$99.10	$99.10
Purchase #2	$134.44	13.828%	$153.0304	$153.03	$153.05	$153.00
Purchase #3	$197.40	10.515%	$218.1566	$218.16	$218.15	$218.20
Purchase #4	$151.33	11.229%	$168.3228	$168.32	$168.30	$168.30
Purchase #5	$63.32	12.267%	$71.0875	$71.09	$71.10	$71.10
Purchase #6	$18.55	13.482%	$21.0509	$21.05	$21.05	$21.10
Purchase #7	$195.61	12.612%	$220.2803	$220.28	$220.30	$220.30
7 purchase totals =	$855.46		$951.0476	$951.05	$951.05	$951.10