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	$242.66	5.380%	$255.7151	$255.72	$255.70	$255.70
Purchase #2	$36.76	9.352%	$40.1978	$40.20	$40.20	$40.20
Purchase #3	$100.80	10.801%	$111.6874	$111.69	$111.70	$111.70
Purchase #4	$151.35	6.599%	$161.3376	$161.34	$161.35	$161.30
Purchase #5	$34.84	9.317%	$38.086	$38.09	$38.10	$38.10
Purchase #6	$84.29	7.135%	$90.3041	$90.30	$90.30	$90.30
Purchase #7	$65.59	5.529%	$69.2165	$69.22	$69.20	$69.20
7 purchase totals =	$716.29		$766.5445	$766.56	$766.55	$766.50