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	$241.25	5.218%	$253.8384	$253.84	$253.85	$253.80
Purchase #2	$47.63	12.736%	$53.6962	$53.70	$53.70	$53.70
Purchase #3	$131.40	11.732%	$146.8158	$146.82	$146.80	$146.80
Purchase #4	$123.53	4.147%	$128.6528	$128.65	$128.65	$128.70
Purchase #5	$33.36	13.158%	$37.7495	$37.75	$37.75	$37.70
Purchase #6	$103.87	10.801%	$115.089	$115.09	$115.10	$115.10
Purchase #7	$20.50	4.556%	$21.434	$21.43	$21.45	$21.40
7 purchase totals =	$701.54		$757.2757	$757.28	$757.30	$757.20