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	$12.46	8.229%	$13.4853	$13.49	$13.50	$13.50
Purchase #2	$194.96	10.471%	$215.3743	$215.37	$215.35	$215.40
Purchase #3	$74.70	11.741%	$83.4705	$83.47	$83.45	$83.50
Purchase #4	$85.42	6.789%	$91.2192	$91.22	$91.20	$91.20
Purchase #5	$59.77	4.349%	$62.3694	$62.37	$62.35	$62.40
Purchase #6	$68.52	4.475%	$71.5863	$71.59	$71.60	$71.60
Purchase #7	$117.28	6.182%	$124.5302	$124.53	$124.55	$124.50
7 purchase totals =	$613.11		$662.0352	$662.04	$662.00	$662.10