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	$140.78	10.805%	$155.9913	$155.99	$156.00	$156.00
Purchase #2	$108.39	12.642%	$122.0927	$122.09	$122.10	$122.10
Purchase #3	$112.29	10.200%	$123.7436	$123.74	$123.75	$123.70
Purchase #4	$240.94	9.682%	$264.2678	$264.27	$264.25	$264.30
Purchase #5	$82.82	8.632%	$89.969	$89.97	$89.95	$90.00
Purchase #6	$120.54	9.276%	$131.7213	$131.72	$131.70	$131.70
Purchase #7	$188.81	5.835%	$199.8271	$199.83	$199.85	$199.80
7 purchase totals =	$994.57		$1,087.6128	$1,087.61	$1,087.60	$1,087.60