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	$238.78	11.217%	$265.564	$265.56	$265.55	$265.60
Purchase #2	$240.89	12.661%	$271.3891	$271.39	$271.40	$271.40
Purchase #3	$182.85	7.631%	$196.8033	$196.80	$196.80	$196.80
Purchase #4	$234.57	12.557%	$264.025	$264.03	$264.05	$264.00
Purchase #5	$226.80	11.491%	$252.8616	$252.86	$252.85	$252.90
Purchase #6	$95.79	4.373%	$99.9789	$99.98	$100.00	$100.00
Purchase #7	$219.48	12.407%	$246.7109	$246.71	$246.70	$246.70
7 purchase totals =	$1,439.16		$1,597.3328	$1,597.33	$1,597.35	$1,597.40