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	$96.36	3.315%	$99.5543	$99.55	$99.55	$99.60
Purchase #2	$115.40	11.249%	$128.3813	$128.38	$128.40	$128.40
Purchase #3	$145.52	8.307%	$157.6083	$157.61	$157.60	$157.60
Purchase #4	$231.29	6.541%	$246.4187	$246.42	$246.40	$246.40
Purchase #5	$25.60	12.185%	$28.7194	$28.72	$28.70	$28.70
Purchase #6	$82.46	10.370%	$91.0111	$91.01	$91.00	$91.00
Purchase #7	$128.45	11.779%	$143.5801	$143.58	$143.60	$143.60
7 purchase totals =	$825.08		$895.2732	$895.27	$895.25	$895.30