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	$31.28	8.115%	$33.8184	$33.82	$33.80	$33.80
Purchase #2	$120.64	6.475%	$128.4514	$128.45	$128.45	$128.50
Purchase #3	$138.72	6.854%	$148.2279	$148.23	$148.25	$148.20
Purchase #4	$73.32	8.733%	$79.723	$79.72	$79.70	$79.70
Purchase #5	$59.48	12.459%	$66.8906	$66.89	$66.90	$66.90
Purchase #6	$144.70	5.104%	$152.0855	$152.09	$152.10	$152.10
Purchase #7	$221.63	9.294%	$242.2283	$242.23	$242.25	$242.20
7 purchase totals =	$789.77		$851.4251	$851.43	$851.45	$851.40