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	$91.71	8.356%	$99.3733	$99.37	$99.35	$99.40
Purchase #2	$38.64	4.373%	$40.3297	$40.33	$40.35	$40.30
Purchase #3	$94.87	8.633%	$103.0601	$103.06	$103.05	$103.10
Purchase #4	$135.79	11.309%	$151.1465	$151.15	$151.15	$151.10
Purchase #5	$151.38	7.586%	$162.8637	$162.86	$162.85	$162.90
Purchase #6	$249.25	5.675%	$263.3949	$263.39	$263.40	$263.40
Purchase #7	$180.89	6.724%	$193.053	$193.05	$193.05	$193.10
7 purchase totals =	$942.53		$1,013.2212	$1,013.21	$1,013.20	$1,013.30