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	$205.76	12.304%	$231.0767	$231.08	$231.10	$231.10
Purchase #2	$72.38	8.630%	$78.6264	$78.63	$78.65	$78.60
Purchase #3	$99.86	5.871%	$105.7228	$105.72	$105.70	$105.70
Purchase #4	$78.46	6.150%	$83.2853	$83.29	$83.30	$83.30
Purchase #5	$221.98	9.121%	$242.2268	$242.23	$242.25	$242.20
Purchase #6	$10.94	9.567%	$11.9866	$11.99	$12.00	$12.00
Purchase #7	$118.65	12.795%	$133.8313	$133.83	$133.85	$133.80
7 purchase totals =	$808.03		$886.7559	$886.77	$886.85	$886.70