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	$143.34	7.663%	$154.3241	$154.32	$154.30	$154.30
Purchase #2	$165.33	9.210%	$180.5569	$180.56	$180.55	$180.60
Purchase #3	$147.50	11.386%	$164.2944	$164.29	$164.30	$164.30
Purchase #4	$219.41	4.738%	$229.8056	$229.81	$229.80	$229.80
Purchase #5	$63.89	12.605%	$71.9433	$71.94	$71.95	$71.90
Purchase #6	$22.47	10.404%	$24.8078	$24.81	$24.80	$24.80
Purchase #7	$145.51	13.860%	$165.6777	$165.68	$165.70	$165.70
7 purchase totals =	$907.45		$991.4098	$991.41	$991.40	$991.40