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	$243.86	6.601%	$259.9572	$259.96	$259.95	$260.00
Purchase #2	$96.75	8.826%	$105.2892	$105.29	$105.30	$105.30
Purchase #3	$93.57	10.771%	$103.6484	$103.65	$103.65	$103.60
Purchase #4	$93.92	3.779%	$97.4692	$97.47	$97.45	$97.50
Purchase #5	$72.72	7.276%	$78.0111	$78.01	$78.00	$78.00
Purchase #6	$181.76	9.538%	$199.0963	$199.10	$199.10	$199.10
Purchase #7	$29.52	7.650%	$31.7783	$31.78	$31.80	$31.80
7 purchase totals =	$812.10		$875.2497	$875.26	$875.25	$875.30