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	$232.38	4.168%	$242.0656	$242.07	$242.05	$242.10
Purchase #2	$188.50	3.846%	$195.7497	$195.75	$195.75	$195.70
Purchase #3	$32.61	12.123%	$36.5633	$36.56	$36.55	$36.60
Purchase #4	$67.93	12.732%	$76.5788	$76.58	$76.60	$76.60
Purchase #5	$73.76	12.755%	$83.1681	$83.17	$83.15	$83.20
Purchase #6	$90.64	9.873%	$99.5889	$99.59	$99.60	$99.60
Purchase #7	$70.60	9.198%	$77.0938	$77.09	$77.10	$77.10
7 purchase totals =	$756.42		$810.8082	$810.81	$810.80	$810.90