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	$153.90	7.361%	$165.2286	$165.23	$165.25	$165.20
Purchase #2	$221.51	8.484%	$240.3029	$240.30	$240.30	$240.30
Purchase #3	$243.93	11.561%	$272.1307	$272.13	$272.15	$272.10
Purchase #4	$20.85	4.276%	$21.7415	$21.74	$21.75	$21.70
Purchase #5	$86.91	4.504%	$90.8244	$90.82	$90.80	$90.80
Purchase #6	$37.98	3.534%	$39.3222	$39.32	$39.30	$39.30
Purchase #7	$148.99	4.602%	$155.8465	$155.85	$155.85	$155.80
7 purchase totals =	$914.07		$985.3968	$985.39	$985.40	$985.20