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	$231.55	6.713%	$247.094	$247.09	$247.10	$247.10
Purchase #2	$91.60	12.134%	$102.7147	$102.71	$102.70	$102.70
Purchase #3	$81.95	10.637%	$90.667	$90.67	$90.65	$90.70
Purchase #4	$56.94	5.166%	$59.8815	$59.88	$59.90	$59.90
Purchase #5	$37.50	4.391%	$39.1466	$39.15	$39.15	$39.10
Purchase #6	$35.46	10.536%	$39.1961	$39.20	$39.20	$39.20
Purchase #7	$210.43	6.290%	$223.666	$223.67	$223.65	$223.70
7 purchase totals =	$745.43		$802.3659	$802.37	$802.35	$802.40