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	$183.35	3.654%	$190.0496	$190.05	$190.05	$190.00
Purchase #2	$131.64	4.338%	$137.3505	$137.35	$137.35	$137.40
Purchase #3	$98.93	3.539%	$102.4311	$102.43	$102.45	$102.40
Purchase #4	$38.27	10.467%	$42.2757	$42.28	$42.30	$42.30
Purchase #5	$229.62	7.318%	$246.4236	$246.42	$246.40	$246.40
Purchase #6	$106.50	11.844%	$119.1139	$119.11	$119.10	$119.10
Purchase #7	$100.52	3.294%	$103.8311	$103.83	$103.85	$103.80
7 purchase totals =	$888.83		$941.4755	$941.47	$941.50	$941.40