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	$38.83	3.594%	$40.2256	$40.23	$40.25	$40.20
Purchase #2	$157.99	10.800%	$175.0529	$175.05	$175.05	$175.10
Purchase #3	$71.92	13.363%	$81.5307	$81.53	$81.55	$81.50
Purchase #4	$84.84	7.195%	$90.9442	$90.94	$90.95	$90.90
Purchase #5	$53.85	10.156%	$59.319	$59.32	$59.30	$59.30
Purchase #6	$152.76	8.152%	$165.213	$165.21	$165.20	$165.20
Purchase #7	$148.75	3.661%	$154.1957	$154.20	$154.20	$154.20
7 purchase totals =	$708.94		$766.4811	$766.48	$766.50	$766.40