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	$128.62	7.728%	$138.5598	$138.56	$138.55	$138.60
Purchase #2	$85.51	8.153%	$92.4816	$92.48	$92.50	$92.50
Purchase #3	$26.47	7.580%	$28.4764	$28.48	$28.50	$28.50
Purchase #4	$72.68	7.519%	$78.1448	$78.14	$78.15	$78.10
Purchase #5	$73.96	4.136%	$77.019	$77.02	$77.00	$77.00
Purchase #6	$142.72	7.838%	$153.9064	$153.91	$153.90	$153.90
Purchase #7	$69.93	4.140%	$72.8251	$72.83	$72.85	$72.80
7 purchase totals =	$599.89		$641.4131	$641.42	$641.45	$641.40