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	$31.79	5.653%	$33.5871	$33.59	$33.60	$33.60
Purchase #2	$25.82	11.839%	$28.8768	$28.88	$28.90	$28.90
Purchase #3	$118.80	13.536%	$134.8808	$134.88	$134.90	$134.90
Purchase #4	$41.82	10.309%	$46.1312	$46.13	$46.15	$46.10
Purchase #5	$77.83	13.588%	$88.4055	$88.41	$88.40	$88.40
Purchase #6	$55.86	12.411%	$62.7928	$62.79	$62.80	$62.80
Purchase #7	$140.81	3.468%	$145.6933	$145.69	$145.70	$145.70
7 purchase totals =	$492.73		$540.3675	$540.37	$540.45	$540.40