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	$11.29	9.659%	$12.3805	$12.38	$12.40	$12.40
Purchase #2	$94.41	6.108%	$100.1766	$100.18	$100.20	$100.20
Purchase #3	$160.32	8.428%	$173.8318	$173.83	$173.85	$173.80
Purchase #4	$40.86	8.331%	$44.264	$44.26	$44.25	$44.30
Purchase #5	$43.29	5.711%	$45.7623	$45.76	$45.75	$45.80
Purchase #6	$46.96	9.860%	$51.5903	$51.59	$51.60	$51.60
Purchase #7	$203.44	3.165%	$209.8789	$209.88	$209.90	$209.90
7 purchase totals =	$600.57		$637.8844	$637.88	$637.95	$638.00