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	$125.86	13.833%	$143.2702	$143.27	$143.25	$143.30
Purchase #2	$154.75	10.852%	$171.5435	$171.54	$171.55	$171.50
Purchase #3	$11.53	7.498%	$12.3945	$12.39	$12.40	$12.40
Purchase #4	$154.65	6.222%	$164.2723	$164.27	$164.25	$164.30
Purchase #5	$39.51	5.778%	$41.7929	$41.79	$41.80	$41.80
Purchase #6	$11.46	12.572%	$12.9008	$12.90	$12.90	$12.90
Purchase #7	$14.37	7.829%	$15.495	$15.50	$15.50	$15.50
7 purchase totals =	$512.13		$561.6692	$561.66	$561.65	$561.70