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	$57.65	3.821%	$59.8528	$59.85	$59.85	$59.90
Purchase #2	$95.27	7.577%	$102.4886	$102.49	$102.50	$102.50
Purchase #3	$97.56	8.132%	$105.4936	$105.49	$105.50	$105.50
Purchase #4	$206.68	12.113%	$231.7151	$231.72	$231.70	$231.70
Purchase #5	$234.93	12.629%	$264.5993	$264.60	$264.60	$264.60
Purchase #6	$26.46	6.749%	$28.2458	$28.25	$28.25	$28.20
Purchase #7	$129.72	8.499%	$140.7449	$140.74	$140.75	$140.70
7 purchase totals =	$848.27		$933.1401	$933.14	$933.15	$933.10