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	$93.57	6.577%	$99.7241	$99.72	$99.70	$99.70
Purchase #2	$137.45	5.311%	$144.75	$144.75	$144.75	$144.80
Purchase #3	$45.50	6.253%	$48.3451	$48.35	$48.35	$48.30
Purchase #4	$183.86	6.572%	$195.9433	$195.94	$195.95	$195.90
Purchase #5	$97.59	13.736%	$110.995	$111.00	$111.00	$111.00
Purchase #6	$239.93	9.155%	$261.8956	$261.90	$261.90	$261.90
Purchase #7	$131.88	10.820%	$146.1494	$146.15	$146.15	$146.10
7 purchase totals =	$929.78		$1,007.8025	$1,007.81	$1,007.80	$1,007.70