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	$61.67	4.828%	$64.6474	$64.65	$64.65	$64.60
Purchase #2	$37.32	3.756%	$38.7217	$38.72	$38.70	$38.70
Purchase #3	$82.56	8.664%	$89.713	$89.71	$89.70	$89.70
Purchase #4	$148.63	13.158%	$168.1867	$168.19	$168.20	$168.20
Purchase #5	$77.95	9.510%	$85.363	$85.36	$85.35	$85.40
Purchase #6	$32.45	4.175%	$33.8048	$33.80	$33.80	$33.80
Purchase #7	$18.50	8.133%	$20.0046	$20.00	$20.00	$20.00
7 purchase totals =	$459.08		$500.4412	$500.43	$500.40	$500.40