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	$172.71	4.455%	$180.4042	$180.40	$180.40	$180.40
Purchase #2	$75.61	13.593%	$85.8877	$85.89	$85.90	$85.90
Purchase #3	$144.63	10.269%	$159.4821	$159.48	$159.50	$159.50
Purchase #4	$65.91	4.302%	$68.7454	$68.75	$68.75	$68.70
Purchase #5	$176.32	5.717%	$186.4002	$186.40	$186.40	$186.40
Purchase #6	$75.74	5.872%	$80.1875	$80.19	$80.20	$80.20
Purchase #7	$64.90	11.477%	$72.3486	$72.35	$72.35	$72.30
7 purchase totals =	$775.82		$833.4557	$833.46	$833.50	$833.40