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	$141.89	5.632%	$149.8812	$149.88	$149.90	$149.90
Purchase #2	$111.85	6.401%	$119.0095	$119.01	$119.00	$119.00
Purchase #3	$85.91	4.603%	$89.8644	$89.86	$89.85	$89.90
Purchase #4	$67.75	13.574%	$76.9464	$76.95	$76.95	$76.90
Purchase #5	$155.63	3.161%	$160.5495	$160.55	$160.55	$160.50
Purchase #6	$208.48	11.838%	$233.1599	$233.16	$233.15	$233.20
Purchase #7	$21.60	10.753%	$23.9226	$23.92	$23.90	$23.90
7 purchase totals =	$793.11		$853.3335	$853.33	$853.30	$853.30