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	$203.51	10.472%	$224.8216	$224.82	$224.80	$224.80
Purchase #2	$154.72	8.491%	$167.8573	$167.86	$167.85	$167.90
Purchase #3	$237.77	9.802%	$261.0762	$261.08	$261.10	$261.10
Purchase #4	$234.79	3.343%	$242.639	$242.64	$242.65	$242.60
Purchase #5	$73.30	6.669%	$78.1884	$78.19	$78.20	$78.20
Purchase #6	$158.61	8.566%	$172.1965	$172.20	$172.20	$172.20
Purchase #7	$150.51	11.184%	$167.343	$167.34	$167.35	$167.30
7 purchase totals =	$1,213.21		$1,314.1220	$1,314.13	$1,314.15	$1,314.10