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	$80.77	11.781%	$90.2855	$90.29	$90.30	$90.30
Purchase #2	$248.99	6.557%	$265.3163	$265.32	$265.30	$265.30
Purchase #3	$38.50	10.250%	$42.4463	$42.45	$42.45	$42.40
Purchase #4	$228.91	4.175%	$238.467	$238.47	$238.45	$238.50
Purchase #5	$206.89	8.607%	$224.697	$224.70	$224.70	$224.70
Purchase #6	$241.52	3.767%	$250.6181	$250.62	$250.60	$250.60
Purchase #7	$10.46	8.789%	$11.3793	$11.38	$11.40	$11.40
7 purchase totals =	$1,056.04		$1,123.2095	$1,123.23	$1,123.20	$1,123.20