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	$81.56	12.638%	$91.8676	$91.87	$91.85	$91.90
Purchase #2	$70.33	6.261%	$74.7334	$74.73	$74.75	$74.70
Purchase #3	$44.26	10.387%	$48.8573	$48.86	$48.85	$48.90
Purchase #4	$196.38	4.620%	$205.4528	$205.45	$205.45	$205.50
Purchase #5	$78.76	13.160%	$89.1248	$89.12	$89.10	$89.10
Purchase #6	$122.92	12.645%	$138.4632	$138.46	$138.45	$138.50
Purchase #7	$160.43	10.148%	$176.7104	$176.71	$176.70	$176.70
7 purchase totals =	$754.64		$825.2095	$825.20	$825.15	$825.30