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	$189.42	3.384%	$195.83	$195.83	$195.85	$195.80
Purchase #2	$149.71	7.433%	$160.8379	$160.84	$160.85	$160.80
Purchase #3	$35.37	9.601%	$38.7659	$38.77	$38.75	$38.80
Purchase #4	$70.25	5.635%	$74.2086	$74.21	$74.20	$74.20
Purchase #5	$38.44	4.786%	$40.2797	$40.28	$40.30	$40.30
Purchase #6	$119.51	4.177%	$124.5019	$124.50	$124.50	$124.50
Purchase #7	$241.72	5.851%	$255.863	$255.86	$255.85	$255.90
7 purchase totals =	$844.42		$890.2870	$890.29	$890.30	$890.30