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	$131.38	9.726%	$144.158	$144.16	$144.15	$144.20
Purchase #2	$153.53	8.415%	$166.4495	$166.45	$166.45	$166.40
Purchase #3	$6.63	12.662%	$7.4695	$7.47	$7.45	$7.50
Purchase #4	$63.34	4.245%	$66.0288	$66.03	$66.05	$66.00
Purchase #5	$134.90	7.409%	$144.8947	$144.89	$144.90	$144.90
Purchase #6	$11.57	12.356%	$12.9996	$13.00	$13.00	$13.00
Purchase #7	$192.94	3.375%	$199.4517	$199.45	$199.45	$199.50
7 purchase totals =	$694.29		$741.4518	$741.45	$741.45	$741.50