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	$173.94	7.432%	$186.8672	$186.87	$186.85	$186.90
Purchase #2	$108.82	10.814%	$120.5878	$120.59	$120.60	$120.60
Purchase #3	$103.33	7.810%	$111.4001	$111.40	$111.40	$111.40
Purchase #4	$210.33	6.542%	$224.0898	$224.09	$224.10	$224.10
Purchase #5	$159.65	6.814%	$170.5286	$170.53	$170.55	$170.50
Purchase #6	$161.86	6.216%	$171.9212	$171.92	$171.90	$171.90
Purchase #7	$224.98	13.500%	$255.3523	$255.35	$255.35	$255.40
7 purchase totals =	$1,142.91		$1,240.7470	$1,240.75	$1,240.75	$1,240.80