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	$136.77	5.302%	$144.0215	$144.02	$144.00	$144.00
Purchase #2	$11.87	5.275%	$12.4961	$12.50	$12.50	$12.50
Purchase #3	$90.95	10.406%	$100.4143	$100.41	$100.40	$100.40
Purchase #4	$57.74	7.587%	$62.1207	$62.12	$62.10	$62.10
Purchase #5	$198.92	11.159%	$221.1175	$221.12	$221.10	$221.10
Purchase #6	$38.38	4.321%	$40.0384	$40.04	$40.05	$40.00
Purchase #7	$29.88	10.110%	$32.9009	$32.90	$32.90	$32.90
7 purchase totals =	$564.51		$613.1094	$613.11	$613.05	$613.00