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	$13.90	8.487%	$15.0797	$15.08	$15.10	$15.10
Purchase #2	$38.25	9.288%	$41.8027	$41.80	$41.80	$41.80
Purchase #3	$101.76	10.118%	$112.0561	$112.06	$112.05	$112.10
Purchase #4	$173.78	10.455%	$191.9487	$191.95	$191.95	$191.90
Purchase #5	$59.94	12.153%	$67.2245	$67.22	$67.20	$67.20
Purchase #6	$67.73	9.253%	$73.9971	$74.00	$74.00	$74.00
Purchase #7	$91.37	9.305%	$99.872	$99.87	$99.85	$99.90
7 purchase totals =	$546.73		$601.9808	$601.98	$601.95	$602.00