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	$72.39	5.556%	$76.412	$76.41	$76.40	$76.40
Purchase #2	$24.86	13.372%	$28.1843	$28.18	$28.20	$28.20
Purchase #3	$215.87	5.349%	$227.4169	$227.42	$227.40	$227.40
Purchase #4	$190.66	13.542%	$216.4792	$216.48	$216.50	$216.50
Purchase #5	$83.55	8.452%	$90.6116	$90.61	$90.60	$90.60
Purchase #6	$194.33	12.802%	$219.2081	$219.21	$219.20	$219.20
Purchase #7	$238.33	11.347%	$265.3733	$265.37	$265.35	$265.40
7 purchase totals =	$1,019.99		$1,123.6854	$1,123.68	$1,123.65	$1,123.70