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	$247.72	13.267%	$280.585	$280.59	$280.60	$280.60
Purchase #2	$158.90	11.851%	$177.7312	$177.73	$177.75	$177.70
Purchase #3	$113.79	5.680%	$120.2533	$120.25	$120.25	$120.30
Purchase #4	$171.29	7.655%	$184.4022	$184.40	$184.40	$184.40
Purchase #5	$63.56	11.232%	$70.6991	$70.70	$70.70	$70.70
Purchase #6	$63.69	13.607%	$72.3563	$72.36	$72.35	$72.40
Purchase #7	$211.58	5.139%	$222.4531	$222.45	$222.45	$222.50
7 purchase totals =	$1,030.53		$1,128.4802	$1,128.48	$1,128.50	$1,128.60