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	$150.54	6.331%	$160.0707	$160.07	$160.05	$160.10
Purchase #2	$43.52	10.585%	$48.1266	$48.13	$48.15	$48.10
Purchase #3	$211.38	10.498%	$233.5707	$233.57	$233.55	$233.60
Purchase #4	$157.25	8.779%	$171.055	$171.06	$171.05	$171.10
Purchase #5	$92.87	6.596%	$98.9957	$99.00	$99.00	$99.00
Purchase #6	$58.88	12.696%	$66.3554	$66.36	$66.35	$66.40
Purchase #7	$137.30	4.522%	$143.5087	$143.51	$143.50	$143.50
7 purchase totals =	$851.74		$921.6828	$921.70	$921.65	$921.80