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	$237.79	10.751%	$263.3548	$263.35	$263.35	$263.40
Purchase #2	$40.54	6.591%	$43.212	$43.21	$43.20	$43.20
Purchase #3	$135.32	4.734%	$141.726	$141.73	$141.75	$141.70
Purchase #4	$82.80	8.190%	$89.5813	$89.58	$89.60	$89.60
Purchase #5	$28.57	4.499%	$29.8554	$29.86	$29.85	$29.90
Purchase #6	$90.28	5.118%	$94.9005	$94.90	$94.90	$94.90
Purchase #7	$247.90	11.190%	$275.64	$275.64	$275.65	$275.60
7 purchase totals =	$863.20		$938.2700	$938.27	$938.30	$938.30