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	$109.69	12.443%	$123.3387	$123.34	$123.35	$123.30
Purchase #2	$75.41	10.699%	$83.4781	$83.48	$83.50	$83.50
Purchase #3	$71.27	11.475%	$79.4482	$79.45	$79.45	$79.40
Purchase #4	$166.52	3.731%	$172.7329	$172.73	$172.75	$172.70
Purchase #5	$6.32	12.170%	$7.0891	$7.09	$7.10	$7.10
Purchase #6	$189.33	11.120%	$210.3835	$210.38	$210.40	$210.40
Purchase #7	$18.31	7.609%	$19.7032	$19.70	$19.70	$19.70
7 purchase totals =	$636.85		$696.1737	$696.17	$696.25	$696.10