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	$75.62	13.595%	$85.9005	$85.90	$85.90	$85.90
Purchase #2	$148.72	4.396%	$155.2577	$155.26	$155.25	$155.30
Purchase #3	$136.48	7.319%	$146.469	$146.47	$146.45	$146.50
Purchase #4	$146.73	6.291%	$155.9608	$155.96	$155.95	$156.00
Purchase #5	$115.50	10.110%	$127.1771	$127.18	$127.20	$127.20
Purchase #6	$95.33	9.812%	$104.6838	$104.68	$104.70	$104.70
Purchase #7	$205.54	7.865%	$221.7057	$221.71	$221.70	$221.70
7 purchase totals =	$923.92		$997.1546	$997.16	$997.15	$997.30