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	$130.54	5.208%	$137.3385	$137.34	$137.35	$137.30
Purchase #2	$36.35	7.326%	$39.013	$39.01	$39.00	$39.00
Purchase #3	$220.72	12.336%	$247.948	$247.95	$247.95	$247.90
Purchase #4	$209.41	9.703%	$229.7291	$229.73	$229.75	$229.70
Purchase #5	$90.54	5.847%	$95.8339	$95.83	$95.85	$95.80
Purchase #6	$127.71	13.321%	$144.7222	$144.72	$144.70	$144.70
Purchase #7	$92.68	11.147%	$103.011	$103.01	$103.00	$103.00
7 purchase totals =	$907.95		$997.5957	$997.59	$997.60	$997.40