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	$38.49	6.328%	$40.9256	$40.93	$40.95	$40.90
Purchase #2	$51.92	13.872%	$59.1223	$59.12	$59.10	$59.10
Purchase #3	$137.61	10.248%	$151.7123	$151.71	$151.70	$151.70
Purchase #4	$48.80	12.287%	$54.7961	$54.80	$54.80	$54.80
Purchase #5	$90.40	13.470%	$102.5769	$102.58	$102.60	$102.60
Purchase #6	$82.66	5.743%	$87.4072	$87.41	$87.40	$87.40
Purchase #7	$134.46	4.720%	$140.8065	$140.81	$140.80	$140.80
7 purchase totals =	$584.34		$637.3469	$637.36	$637.35	$637.30