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	$143.89	11.604%	$160.587	$160.59	$160.60	$160.60
Purchase #2	$82.71	7.816%	$89.1746	$89.17	$89.15	$89.20
Purchase #3	$21.91	5.564%	$23.1291	$23.13	$23.15	$23.10
Purchase #4	$201.32	11.773%	$225.0214	$225.02	$225.00	$225.00
Purchase #5	$110.37	9.240%	$120.5682	$120.57	$120.55	$120.60
Purchase #6	$143.94	9.233%	$157.23	$157.23	$157.25	$157.20
Purchase #7	$125.34	13.709%	$142.5229	$142.52	$142.50	$142.50
7 purchase totals =	$829.48		$918.2332	$918.23	$918.20	$918.20