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	$89.70	3.804%	$93.1122	$93.11	$93.10	$93.10
Purchase #2	$90.60	10.246%	$99.8829	$99.88	$99.90	$99.90
Purchase #3	$113.37	4.707%	$118.7063	$118.71	$118.70	$118.70
Purchase #4	$236.59	8.864%	$257.5613	$257.56	$257.55	$257.60
Purchase #5	$44.59	6.129%	$47.3229	$47.32	$47.30	$47.30
Purchase #6	$40.31	7.474%	$43.3228	$43.32	$43.30	$43.30
Purchase #7	$103.74	5.598%	$109.5474	$109.55	$109.55	$109.50
7 purchase totals =	$718.90		$769.4558	$769.45	$769.40	$769.40