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	$89.62	12.380%	$100.715	$100.72	$100.70	$100.70
Purchase #2	$142.37	10.656%	$157.5409	$157.54	$157.55	$157.50
Purchase #3	$250.26	13.534%	$284.1302	$284.13	$284.15	$284.10
Purchase #4	$48.75	4.567%	$50.9764	$50.98	$51.00	$51.00
Purchase #5	$195.31	5.302%	$205.6653	$205.67	$205.65	$205.70
Purchase #6	$18.82	7.533%	$20.2377	$20.24	$20.25	$20.20
Purchase #7	$154.33	9.419%	$168.8663	$168.87	$168.85	$168.90
7 purchase totals =	$899.46		$988.1318	$988.15	$988.15	$988.10