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	$162.49	9.759%	$178.3474	$178.35	$178.35	$178.30
Purchase #2	$146.84	8.555%	$159.4022	$159.40	$159.40	$159.40
Purchase #3	$229.93	13.723%	$261.4833	$261.48	$261.50	$261.50
Purchase #4	$188.89	7.547%	$203.1455	$203.15	$203.15	$203.10
Purchase #5	$80.93	11.673%	$90.377	$90.38	$90.40	$90.40
Purchase #6	$32.49	3.173%	$33.5209	$33.52	$33.50	$33.50
Purchase #7	$64.57	13.367%	$73.2011	$73.20	$73.20	$73.20
7 purchase totals =	$906.14		$999.4774	$999.48	$999.50	$999.40