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	$134.72	10.139%	$148.3793	$148.38	$148.40	$148.40
Purchase #2	$57.69	4.676%	$60.3876	$60.39	$60.40	$60.40
Purchase #3	$228.69	11.721%	$255.4948	$255.49	$255.50	$255.50
Purchase #4	$162.59	3.451%	$168.201	$168.20	$168.20	$168.20
Purchase #5	$142.66	7.851%	$153.8602	$153.86	$153.85	$153.90
Purchase #6	$164.52	8.272%	$178.1291	$178.13	$178.15	$178.10
Purchase #7	$168.46	13.299%	$190.8635	$190.86	$190.85	$190.90
7 purchase totals =	$1,059.33		$1,155.3155	$1,155.31	$1,155.35	$1,155.40