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	$89.94	10.439%	$99.3288	$99.33	$99.35	$99.30
Purchase #2	$249.99	3.724%	$259.2996	$259.30	$259.30	$259.30
Purchase #3	$167.89	8.317%	$181.8534	$181.85	$181.85	$181.90
Purchase #4	$178.65	5.481%	$188.4418	$188.44	$188.45	$188.40
Purchase #5	$13.49	6.648%	$14.3868	$14.39	$14.40	$14.40
Purchase #6	$237.76	10.859%	$263.5784	$263.58	$263.60	$263.60
Purchase #7	$245.45	12.407%	$275.903	$275.90	$275.90	$275.90
7 purchase totals =	$1,183.17		$1,282.7918	$1,282.79	$1,282.85	$1,282.80