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	$155.50	10.338%	$171.5756	$171.58	$171.60	$171.60
Purchase #2	$172.66	6.270%	$183.4858	$183.49	$183.50	$183.50
Purchase #3	$195.90	13.487%	$222.321	$222.32	$222.30	$222.30
Purchase #4	$212.95	4.123%	$221.7299	$221.73	$221.75	$221.70
Purchase #5	$20.74	8.551%	$22.5135	$22.51	$22.50	$22.50
Purchase #6	$155.34	10.337%	$171.3975	$171.40	$171.40	$171.40
Purchase #7	$74.37	6.712%	$79.3617	$79.36	$79.35	$79.40
7 purchase totals =	$987.46		$1,072.3850	$1,072.39	$1,072.40	$1,072.40