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	$99.79	13.594%	$113.3555	$113.36	$113.35	$113.40
Purchase #2	$68.88	4.215%	$71.7833	$71.78	$71.80	$71.80
Purchase #3	$148.54	9.514%	$162.6721	$162.67	$162.65	$162.70
Purchase #4	$56.65	5.674%	$59.8643	$59.86	$59.85	$59.90
Purchase #5	$92.70	9.403%	$101.4166	$101.42	$101.40	$101.40
Purchase #6	$232.60	5.498%	$245.3883	$245.39	$245.40	$245.40
Purchase #7	$9.67	7.810%	$10.4252	$10.43	$10.45	$10.40
7 purchase totals =	$708.83		$764.9053	$764.91	$764.90	$765.00