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	$52.74	7.622%	$56.7598	$56.76	$56.75	$56.80
Purchase #2	$226.29	3.218%	$233.572	$233.57	$233.55	$233.60
Purchase #3	$112.84	4.800%	$118.2563	$118.26	$118.25	$118.30
Purchase #4	$164.83	4.152%	$171.6737	$171.67	$171.65	$171.70
Purchase #5	$65.68	10.523%	$72.5915	$72.59	$72.60	$72.60
Purchase #6	$72.41	13.639%	$82.286	$82.29	$82.30	$82.30
Purchase #7	$226.40	7.468%	$243.3076	$243.31	$243.30	$243.30
7 purchase totals =	$921.19		$978.4469	$978.45	$978.40	$978.60