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	$144.75	7.347%	$155.3848	$155.38	$155.40	$155.40
Purchase #2	$36.38	6.650%	$38.7993	$38.80	$38.80	$38.80
Purchase #3	$139.68	9.244%	$152.592	$152.59	$152.60	$152.60
Purchase #4	$40.73	8.472%	$44.1806	$44.18	$44.20	$44.20
Purchase #5	$85.94	4.345%	$89.6741	$89.67	$89.65	$89.70
Purchase #6	$118.35	8.177%	$128.0275	$128.03	$128.05	$128.00
Purchase #7	$245.42	11.566%	$273.8053	$273.81	$273.80	$273.80
7 purchase totals =	$811.25		$882.4636	$882.46	$882.50	$882.50