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	$82.50	8.843%	$89.7955	$89.80	$89.80	$89.80
Purchase #2	$137.90	7.757%	$148.5969	$148.60	$148.60	$148.60
Purchase #3	$87.45	13.702%	$99.4324	$99.43	$99.45	$99.40
Purchase #4	$79.46	5.278%	$83.6539	$83.65	$83.65	$83.70
Purchase #5	$132.93	3.266%	$137.2715	$137.27	$137.25	$137.30
Purchase #6	$161.65	6.474%	$172.1152	$172.12	$172.10	$172.10
Purchase #7	$201.68	4.363%	$210.4793	$210.48	$210.50	$210.50
7 purchase totals =	$883.57		$941.3447	$941.35	$941.35	$941.40