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	$20.50	4.358%	$21.3934	$21.39	$21.40	$21.40
Purchase #2	$86.66	5.437%	$91.3717	$91.37	$91.35	$91.40
Purchase #3	$115.95	5.482%	$122.3064	$122.31	$122.30	$122.30
Purchase #4	$184.60	6.409%	$196.431	$196.43	$196.45	$196.40
Purchase #5	$166.29	5.327%	$175.1483	$175.15	$175.15	$175.10
Purchase #6	$23.81	6.740%	$25.4148	$25.41	$25.40	$25.40
Purchase #7	$76.45	3.131%	$78.8436	$78.84	$78.85	$78.80
7 purchase totals =	$674.26		$710.9092	$710.90	$710.90	$710.80