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	$225.78	12.667%	$254.3796	$254.38	$254.40	$254.40
Purchase #2	$228.45	3.433%	$236.2927	$236.29	$236.30	$236.30
Purchase #3	$168.38	9.110%	$183.7194	$183.72	$183.70	$183.70
Purchase #4	$54.40	3.778%	$56.4552	$56.46	$56.45	$56.50
Purchase #5	$186.82	9.793%	$205.1153	$205.12	$205.10	$205.10
Purchase #6	$78.44	6.297%	$83.3794	$83.38	$83.40	$83.40
Purchase #7	$64.69	3.221%	$66.7737	$66.77	$66.75	$66.80
7 purchase totals =	$1,006.96		$1,086.1153	$1,086.12	$1,086.10	$1,086.20