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	$113.36	12.128%	$127.1083	$127.11	$127.10	$127.10
Purchase #2	$154.40	5.266%	$162.5307	$162.53	$162.55	$162.50
Purchase #3	$120.39	11.572%	$134.3215	$134.32	$134.30	$134.30
Purchase #4	$33.74	3.285%	$34.8484	$34.85	$34.85	$34.80
Purchase #5	$37.41	5.846%	$39.597	$39.60	$39.60	$39.60
Purchase #6	$190.83	8.227%	$206.5296	$206.53	$206.55	$206.50
Purchase #7	$54.50	13.370%	$61.7867	$61.79	$61.80	$61.80
7 purchase totals =	$704.63		$766.7222	$766.73	$766.75	$766.60