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	$177.71	12.868%	$200.5777	$200.58	$200.60	$200.60
Purchase #2	$61.75	13.416%	$70.0344	$70.03	$70.05	$70.00
Purchase #3	$89.79	10.612%	$99.3185	$99.32	$99.30	$99.30
Purchase #4	$128.36	11.860%	$143.5835	$143.58	$143.60	$143.60
Purchase #5	$76.73	13.629%	$87.1875	$87.19	$87.20	$87.20
Purchase #6	$6.65	10.451%	$7.345	$7.35	$7.35	$7.30
Purchase #7	$51.42	11.651%	$57.4109	$57.41	$57.40	$57.40
7 purchase totals =	$592.41		$665.4575	$665.46	$665.50	$665.40