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	$95.88	12.796%	$108.1488	$108.15	$108.15	$108.10
Purchase #2	$81.68	9.843%	$89.7198	$89.72	$89.70	$89.70
Purchase #3	$95.81	11.626%	$106.9489	$106.95	$106.95	$106.90
Purchase #4	$210.40	13.190%	$238.1518	$238.15	$238.15	$238.20
Purchase #5	$158.77	12.360%	$178.394	$178.39	$178.40	$178.40
Purchase #6	$123.85	12.231%	$138.9981	$139.00	$139.00	$139.00
Purchase #7	$214.34	3.826%	$222.5406	$222.54	$222.55	$222.50
7 purchase totals =	$980.73		$1,082.9020	$1,082.90	$1,082.90	$1,082.80