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	$48.94	11.171%	$54.4071	$54.41	$54.40	$54.40
Purchase #2	$129.66	8.533%	$140.7239	$140.72	$140.70	$140.70
Purchase #3	$155.92	8.228%	$168.7491	$168.75	$168.75	$168.70
Purchase #4	$116.83	13.103%	$132.1382	$132.14	$132.15	$132.10
Purchase #5	$37.57	3.501%	$38.8853	$38.89	$38.90	$38.90
Purchase #6	$65.31	10.287%	$72.0284	$72.03	$72.05	$72.00
Purchase #7	$114.94	12.726%	$129.5673	$129.57	$129.55	$129.60
7 purchase totals =	$669.17		$736.4993	$736.51	$736.50	$736.40