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	$246.60	3.366%	$254.9006	$254.90	$254.90	$254.90
Purchase #2	$85.28	12.240%	$95.7183	$95.72	$95.70	$95.70
Purchase #3	$97.38	11.843%	$108.9127	$108.91	$108.90	$108.90
Purchase #4	$82.42	11.376%	$91.7961	$91.80	$91.80	$91.80
Purchase #5	$128.82	10.627%	$142.5097	$142.51	$142.50	$142.50
Purchase #6	$30.30	6.234%	$32.1889	$32.19	$32.20	$32.20
Purchase #7	$33.51	3.104%	$34.5502	$34.55	$34.55	$34.60
7 purchase totals =	$704.31		$760.5765	$760.58	$760.55	$760.60