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	$213.30	13.170%	$241.3916	$241.39	$241.40	$241.40
Purchase #2	$93.27	11.666%	$104.1509	$104.15	$104.15	$104.20
Purchase #3	$232.80	4.710%	$243.7649	$243.76	$243.75	$243.80
Purchase #4	$155.91	6.175%	$165.5374	$165.54	$165.55	$165.50
Purchase #5	$63.86	10.388%	$70.4938	$70.49	$70.50	$70.50
Purchase #6	$75.70	9.140%	$82.619	$82.62	$82.60	$82.60
Purchase #7	$70.85	13.450%	$80.3793	$80.38	$80.40	$80.40
7 purchase totals =	$905.69		$988.3369	$988.33	$988.35	$988.40