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	$86.80	4.521%	$90.7242	$90.72	$90.70	$90.70
Purchase #2	$198.84	3.518%	$205.8352	$205.84	$205.85	$205.80
Purchase #3	$209.90	10.223%	$231.3581	$231.36	$231.35	$231.40
Purchase #4	$159.25	12.496%	$179.1499	$179.15	$179.15	$179.10
Purchase #5	$206.40	8.265%	$223.459	$223.46	$223.45	$223.50
Purchase #6	$243.79	5.455%	$257.0887	$257.09	$257.10	$257.10
Purchase #7	$38.39	12.381%	$43.1431	$43.14	$43.15	$43.10
7 purchase totals =	$1,143.37		$1,230.7582	$1,230.76	$1,230.75	$1,230.70