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	$39.93	10.293%	$44.04	$44.04	$44.05	$44.00
Purchase #2	$185.53	3.457%	$191.9438	$191.94	$191.95	$191.90
Purchase #3	$214.91	7.675%	$231.4043	$231.40	$231.40	$231.40
Purchase #4	$18.56	7.835%	$20.0142	$20.01	$20.00	$20.00
Purchase #5	$191.40	4.236%	$199.5077	$199.51	$199.50	$199.50
Purchase #6	$203.59	8.283%	$220.4534	$220.45	$220.45	$220.50
Purchase #7	$147.46	7.259%	$158.1641	$158.16	$158.15	$158.20
7 purchase totals =	$1,001.38		$1,065.5275	$1,065.51	$1,065.50	$1,065.50