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	$101.59	10.796%	$112.5577	$112.56	$112.55	$112.60
Purchase #2	$151.52	11.769%	$169.3524	$169.35	$169.35	$169.40
Purchase #3	$63.76	10.537%	$70.4784	$70.48	$70.50	$70.50
Purchase #4	$96.91	5.552%	$102.2904	$102.29	$102.30	$102.30
Purchase #5	$36.82	6.704%	$39.2884	$39.29	$39.30	$39.30
Purchase #6	$183.29	12.273%	$205.7852	$205.79	$205.80	$205.80
Purchase #7	$99.53	5.813%	$105.3157	$105.32	$105.30	$105.30
7 purchase totals =	$733.42		$805.0682	$805.08	$805.10	$805.20