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	$81.64	11.807%	$91.2792	$91.28	$91.30	$91.30
Purchase #2	$112.46	12.238%	$126.2229	$126.22	$126.20	$126.20
Purchase #3	$69.61	5.605%	$73.5116	$73.51	$73.50	$73.50
Purchase #4	$234.43	10.695%	$259.5023	$259.50	$259.50	$259.50
Purchase #5	$81.62	10.661%	$90.3215	$90.32	$90.30	$90.30
Purchase #6	$115.97	10.805%	$128.5006	$128.50	$128.50	$128.50
Purchase #7	$199.53	7.801%	$215.0953	$215.10	$215.10	$215.10
7 purchase totals =	$895.26		$984.4334	$984.43	$984.40	$984.40