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	$155.55	7.660%	$167.4651	$167.47	$167.45	$167.50
Purchase #2	$227.89	12.458%	$256.2805	$256.28	$256.30	$256.30
Purchase #3	$228.77	6.548%	$243.7499	$243.75	$243.75	$243.70
Purchase #4	$65.88	9.109%	$71.881	$71.88	$71.90	$71.90
Purchase #5	$118.56	9.256%	$129.5339	$129.53	$129.55	$129.50
Purchase #6	$154.57	13.616%	$175.6163	$175.62	$175.60	$175.60
Purchase #7	$247.61	12.825%	$279.366	$279.37	$279.35	$279.40
7 purchase totals =	$1,198.83		$1,323.8927	$1,323.90	$1,323.90	$1,323.90