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	$86.90	3.575%	$90.0067	$90.01	$90.00	$90.00
Purchase #2	$168.85	6.289%	$179.469	$179.47	$179.45	$179.50
Purchase #3	$27.41	5.617%	$28.9496	$28.95	$28.95	$28.90
Purchase #4	$227.74	13.532%	$258.5578	$258.56	$258.55	$258.60
Purchase #5	$9.66	8.320%	$10.4637	$10.46	$10.45	$10.50
Purchase #6	$42.82	6.460%	$45.5862	$45.59	$45.60	$45.60
Purchase #7	$7.59	7.689%	$8.1736	$8.17	$8.15	$8.20
7 purchase totals =	$570.97		$621.2066	$621.21	$621.15	$621.30