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	$82.42	9.837%	$90.5277	$90.53	$90.55	$90.50
Purchase #2	$41.26	8.122%	$44.6111	$44.61	$44.60	$44.60
Purchase #3	$62.78	6.385%	$66.7885	$66.79	$66.80	$66.80
Purchase #4	$180.35	10.770%	$199.7737	$199.77	$199.75	$199.80
Purchase #5	$136.85	7.303%	$146.8442	$146.84	$146.85	$146.80
Purchase #6	$205.44	7.747%	$221.3554	$221.36	$221.35	$221.40
Purchase #7	$79.79	11.555%	$89.0097	$89.01	$89.00	$89.00
7 purchase totals =	$788.89		$858.9103	$858.91	$858.90	$858.90