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	$224.31	11.131%	$249.2779	$249.28	$249.30	$249.30
Purchase #2	$99.61	7.794%	$107.3736	$107.37	$107.35	$107.40
Purchase #3	$100.82	8.829%	$109.7214	$109.72	$109.70	$109.70
Purchase #4	$37.78	13.165%	$42.7537	$42.75	$42.75	$42.80
Purchase #5	$109.66	13.572%	$124.5431	$124.54	$124.55	$124.50
Purchase #6	$108.66	5.725%	$114.8808	$114.88	$114.90	$114.90
Purchase #7	$20.93	3.197%	$21.5991	$21.60	$21.60	$21.60
7 purchase totals =	$701.77		$770.1496	$770.14	$770.15	$770.20