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	$236.98	3.766%	$245.9047	$245.90	$245.90	$245.90
Purchase #2	$63.46	13.464%	$72.0043	$72.00	$72.00	$72.00
Purchase #3	$102.38	9.358%	$111.9607	$111.96	$111.95	$112.00
Purchase #4	$25.69	11.597%	$28.6693	$28.67	$28.65	$28.70
Purchase #5	$135.69	4.346%	$141.5871	$141.59	$141.60	$141.60
Purchase #6	$156.91	5.782%	$165.9825	$165.98	$166.00	$166.00
Purchase #7	$198.66	8.485%	$215.5163	$215.52	$215.50	$215.50
7 purchase totals =	$919.77		$981.6249	$981.62	$981.60	$981.70