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	$116.91	8.780%	$127.1747	$127.17	$127.15	$127.20
Purchase #2	$101.84	6.514%	$108.4739	$108.47	$108.45	$108.50
Purchase #3	$148.57	10.617%	$164.3437	$164.34	$164.35	$164.30
Purchase #4	$128.48	9.847%	$141.1314	$141.13	$141.15	$141.10
Purchase #5	$218.43	13.490%	$247.8962	$247.90	$247.90	$247.90
Purchase #6	$71.54	10.866%	$79.3135	$79.31	$79.30	$79.30
Purchase #7	$11.48	9.252%	$12.5421	$12.54	$12.55	$12.50
7 purchase totals =	$797.25		$880.8755	$880.86	$880.85	$880.80