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	$121.58	10.567%	$134.4274	$134.43	$134.45	$134.40
Purchase #2	$51.58	4.499%	$53.9006	$53.90	$53.90	$53.90
Purchase #3	$202.79	6.516%	$216.0038	$216.00	$216.00	$216.00
Purchase #4	$142.40	6.867%	$152.1786	$152.18	$152.20	$152.20
Purchase #5	$156.46	10.328%	$172.6192	$172.62	$172.60	$172.60
Purchase #6	$55.58	7.328%	$59.6529	$59.65	$59.65	$59.70
Purchase #7	$69.45	11.318%	$77.3104	$77.31	$77.30	$77.30
7 purchase totals =	$799.84		$866.0929	$866.09	$866.10	$866.10