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	$244.47	8.183%	$264.475	$264.48	$264.50	$264.50
Purchase #2	$199.77	10.689%	$221.1234	$221.12	$221.10	$221.10
Purchase #3	$237.66	13.435%	$269.5896	$269.59	$269.60	$269.60
Purchase #4	$95.34	11.863%	$106.6502	$106.65	$106.65	$106.70
Purchase #5	$134.42	9.304%	$146.9264	$146.93	$146.95	$146.90
Purchase #6	$227.50	9.451%	$249.001	$249.00	$249.00	$249.00
Purchase #7	$37.68	13.763%	$42.8659	$42.87	$42.85	$42.90
7 purchase totals =	$1,176.84		$1,300.6315	$1,300.64	$1,300.65	$1,300.70