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	$97.66	6.317%	$103.8292	$103.83	$103.85	$103.80
Purchase #2	$91.42	9.104%	$99.7429	$99.74	$99.75	$99.70
Purchase #3	$177.86	4.360%	$185.6147	$185.61	$185.60	$185.60
Purchase #4	$210.34	10.705%	$232.8569	$232.86	$232.85	$232.90
Purchase #5	$17.62	4.808%	$18.4672	$18.47	$18.45	$18.50
Purchase #6	$191.58	13.250%	$216.9644	$216.96	$216.95	$217.00
Purchase #7	$59.53	13.429%	$67.5243	$67.52	$67.50	$67.50
7 purchase totals =	$846.01		$924.9996	$924.99	$924.95	$925.00