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	$138.79	3.492%	$143.6365	$143.64	$143.65	$143.60
Purchase #2	$88.48	12.458%	$99.5028	$99.50	$99.50	$99.50
Purchase #3	$191.34	13.132%	$216.4668	$216.47	$216.45	$216.50
Purchase #4	$69.81	3.575%	$72.3057	$72.31	$72.30	$72.30
Purchase #5	$64.57	7.249%	$69.2507	$69.25	$69.25	$69.30
Purchase #6	$120.32	10.415%	$132.8513	$132.85	$132.85	$132.90
Purchase #7	$53.31	3.456%	$55.1524	$55.15	$55.15	$55.20
7 purchase totals =	$726.62		$789.1662	$789.17	$789.15	$789.30