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	$52.94	8.208%	$57.2853	$57.29	$57.30	$57.30
Purchase #2	$36.92	6.475%	$39.3106	$39.31	$39.30	$39.30
Purchase #3	$242.81	10.833%	$269.1136	$269.11	$269.10	$269.10
Purchase #4	$163.29	5.499%	$172.2693	$172.27	$172.25	$172.30
Purchase #5	$28.30	13.389%	$32.0891	$32.09	$32.10	$32.10
Purchase #6	$246.83	10.812%	$273.5173	$273.52	$273.50	$273.50
Purchase #7	$95.52	4.816%	$100.1202	$100.12	$100.10	$100.10
7 purchase totals =	$866.61		$943.7054	$943.71	$943.65	$943.70