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	$32.35	3.674%	$33.5385	$33.54	$33.55	$33.50
Purchase #2	$101.68	11.156%	$113.0234	$113.02	$113.00	$113.00
Purchase #3	$100.53	10.571%	$111.157	$111.16	$111.15	$111.20
Purchase #4	$137.96	8.397%	$149.5445	$149.54	$149.55	$149.50
Purchase #5	$180.75	13.758%	$205.6176	$205.62	$205.60	$205.60
Purchase #6	$115.39	7.109%	$123.5931	$123.59	$123.60	$123.60
Purchase #7	$195.74	7.226%	$209.8842	$209.88	$209.90	$209.90
7 purchase totals =	$864.40		$946.3583	$946.35	$946.35	$946.30