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	$122.75	10.396%	$135.5111	$135.51	$135.50	$135.50
Purchase #2	$162.86	3.274%	$168.192	$168.19	$168.20	$168.20
Purchase #3	$134.91	6.112%	$143.1557	$143.16	$143.15	$143.20
Purchase #4	$37.33	6.514%	$39.7617	$39.76	$39.75	$39.80
Purchase #5	$80.56	11.497%	$89.822	$89.82	$89.80	$89.80
Purchase #6	$135.69	12.233%	$152.289	$152.29	$152.30	$152.30
Purchase #7	$32.43	4.716%	$33.9594	$33.96	$33.95	$34.00
7 purchase totals =	$706.53		$762.6909	$762.69	$762.65	$762.80