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	$18.90	3.375%	$19.5379	$19.54	$19.55	$19.50
Purchase #2	$27.96	13.742%	$31.8023	$31.80	$31.80	$31.80
Purchase #3	$128.29	8.846%	$139.6385	$139.64	$139.65	$139.60
Purchase #4	$201.80	5.561%	$213.0221	$213.02	$213.00	$213.00
Purchase #5	$119.79	6.516%	$127.5955	$127.60	$127.60	$127.60
Purchase #6	$38.89	6.741%	$41.5116	$41.51	$41.50	$41.50
Purchase #7	$10.50	5.375%	$11.0644	$11.06	$11.05	$11.10
7 purchase totals =	$546.13		$584.1723	$584.17	$584.15	$584.10