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	$80.43	12.355%	$90.3671	$90.37	$90.35	$90.40
Purchase #2	$22.60	10.521%	$24.9777	$24.98	$25.00	$25.00
Purchase #3	$123.29	3.132%	$127.1514	$127.15	$127.15	$127.20
Purchase #4	$182.44	6.724%	$194.7073	$194.71	$194.70	$194.70
Purchase #5	$67.89	11.802%	$75.9024	$75.90	$75.90	$75.90
Purchase #6	$101.76	6.243%	$108.1129	$108.11	$108.10	$108.10
Purchase #7	$132.86	7.402%	$142.6943	$142.69	$142.70	$142.70
7 purchase totals =	$711.27		$763.9131	$763.91	$763.90	$764.00