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	$129.71	13.586%	$147.3324	$147.33	$147.35	$147.30
Purchase #2	$161.60	6.546%	$172.1783	$172.18	$172.20	$172.20
Purchase #3	$143.89	8.630%	$156.3077	$156.31	$156.30	$156.30
Purchase #4	$104.41	8.642%	$113.4331	$113.43	$113.45	$113.40
Purchase #5	$11.82	6.540%	$12.593	$12.59	$12.60	$12.60
Purchase #6	$40.40	8.498%	$43.8332	$43.83	$43.85	$43.80
Purchase #7	$154.69	10.448%	$170.852	$170.85	$170.85	$170.90
7 purchase totals =	$746.52		$816.5297	$816.52	$816.60	$816.50