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	$106.97	4.291%	$111.5601	$111.56	$111.55	$111.60
Purchase #2	$119.30	11.578%	$133.1126	$133.11	$133.10	$133.10
Purchase #3	$80.38	3.867%	$83.4883	$83.49	$83.50	$83.50
Purchase #4	$61.71	8.420%	$66.906	$66.91	$66.90	$66.90
Purchase #5	$237.78	13.209%	$269.1884	$269.19	$269.20	$269.20
Purchase #6	$9.59	12.737%	$10.8115	$10.81	$10.80	$10.80
Purchase #7	$183.82	13.335%	$208.3324	$208.33	$208.35	$208.30
7 purchase totals =	$799.55		$883.3993	$883.40	$883.40	$883.40