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	$84.33	5.737%	$89.168	$89.17	$89.15	$89.20
Purchase #2	$112.50	10.344%	$124.137	$124.14	$124.15	$124.10
Purchase #3	$50.31	9.115%	$54.8958	$54.90	$54.90	$54.90
Purchase #4	$79.53	3.526%	$82.3342	$82.33	$82.35	$82.30
Purchase #5	$74.49	7.504%	$80.0797	$80.08	$80.10	$80.10
Purchase #6	$204.34	13.815%	$232.5696	$232.57	$232.55	$232.60
Purchase #7	$140.96	13.232%	$159.6118	$159.61	$159.60	$159.60
7 purchase totals =	$746.46		$822.7961	$822.80	$822.80	$822.80