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	$100.68	9.576%	$110.3211	$110.32	$110.30	$110.30
Purchase #2	$31.53	6.520%	$33.5858	$33.59	$33.60	$33.60
Purchase #3	$148.63	13.550%	$168.7694	$168.77	$168.75	$168.80
Purchase #4	$33.38	12.346%	$37.5011	$37.50	$37.50	$37.50
Purchase #5	$199.70	4.625%	$208.9361	$208.94	$208.95	$208.90
Purchase #6	$91.84	13.505%	$104.243	$104.24	$104.25	$104.20
Purchase #7	$171.26	10.117%	$188.5864	$188.59	$188.60	$188.60
7 purchase totals =	$777.02		$851.9429	$851.95	$851.95	$851.90