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	$121.91	10.174%	$134.3131	$134.31	$134.30	$134.30
Purchase #2	$95.68	5.232%	$100.686	$100.69	$100.70	$100.70
Purchase #3	$42.51	10.308%	$46.8919	$46.89	$46.90	$46.90
Purchase #4	$204.86	12.834%	$231.1517	$231.15	$231.15	$231.20
Purchase #5	$45.62	7.207%	$48.9078	$48.91	$48.90	$48.90
Purchase #6	$56.26	10.819%	$62.3468	$62.35	$62.35	$62.30
Purchase #7	$101.67	4.842%	$106.5929	$106.59	$106.60	$106.60
7 purchase totals =	$668.51		$730.8902	$730.89	$730.90	$730.90