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	$238.66	13.338%	$270.4925	$270.49	$270.50	$270.50
Purchase #2	$181.72	4.794%	$190.4317	$190.43	$190.45	$190.40
Purchase #3	$7.42	5.831%	$7.8527	$7.85	$7.85	$7.90
Purchase #4	$57.45	3.728%	$59.5917	$59.59	$59.60	$59.60
Purchase #5	$90.54	4.761%	$94.8506	$94.85	$94.85	$94.90
Purchase #6	$104.71	11.274%	$116.515	$116.52	$116.50	$116.50
Purchase #7	$242.54	9.508%	$265.6007	$265.60	$265.60	$265.60
7 purchase totals =	$923.04		$1,005.3349	$1,005.33	$1,005.35	$1,005.40