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	$81.98	13.141%	$92.753	$92.75	$92.75	$92.80
Purchase #2	$232.81	3.288%	$240.4648	$240.46	$240.45	$240.50
Purchase #3	$94.62	5.249%	$99.5866	$99.59	$99.60	$99.60
Purchase #4	$237.55	8.750%	$258.3356	$258.34	$258.35	$258.30
Purchase #5	$246.52	3.654%	$255.5278	$255.53	$255.55	$255.50
Purchase #6	$160.98	4.350%	$167.9826	$167.98	$168.00	$168.00
Purchase #7	$142.94	11.317%	$159.1165	$159.12	$159.10	$159.10
7 purchase totals =	$1,197.40		$1,273.7669	$1,273.77	$1,273.80	$1,273.80