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	$35.67	6.621%	$38.0317	$38.03	$38.05	$38.00
Purchase #2	$140.60	13.868%	$160.0984	$160.10	$160.10	$160.10
Purchase #3	$71.81	9.530%	$78.6535	$78.65	$78.65	$78.70
Purchase #4	$6.86	8.320%	$7.4308	$7.43	$7.45	$7.40
Purchase #5	$93.78	6.341%	$99.7266	$99.73	$99.75	$99.70
Purchase #6	$71.53	3.144%	$73.7789	$73.78	$73.80	$73.80
Purchase #7	$107.26	11.452%	$119.5434	$119.54	$119.55	$119.50
7 purchase totals =	$527.51		$577.2633	$577.26	$577.35	$577.20