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	$54.38	13.605%	$61.7784	$61.78	$61.80	$61.80
Purchase #2	$98.84	4.490%	$103.2779	$103.28	$103.30	$103.30
Purchase #3	$91.25	10.335%	$100.6807	$100.68	$100.70	$100.70
Purchase #4	$209.79	10.365%	$231.5347	$231.53	$231.55	$231.50
Purchase #5	$73.67	5.179%	$77.4854	$77.49	$77.50	$77.50
Purchase #6	$177.71	4.144%	$185.0743	$185.07	$185.05	$185.10
Purchase #7	$209.86	4.666%	$219.6521	$219.65	$219.65	$219.70
7 purchase totals =	$915.50		$979.4835	$979.48	$979.55	$979.60