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	$81.60	10.120%	$89.8579	$89.86	$89.85	$89.90
Purchase #2	$176.78	7.781%	$190.5353	$190.54	$190.55	$190.50
Purchase #3	$73.33	4.839%	$76.8784	$76.88	$76.90	$76.90
Purchase #4	$87.37	5.132%	$91.8538	$91.85	$91.85	$91.90
Purchase #5	$75.35	5.370%	$79.3963	$79.40	$79.40	$79.40
Purchase #6	$161.66	12.249%	$181.4617	$181.46	$181.45	$181.50
Purchase #7	$77.69	12.518%	$87.4152	$87.42	$87.40	$87.40
7 purchase totals =	$733.78		$797.3986	$797.41	$797.40	$797.50