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	$33.37	13.540%	$37.8883	$37.89	$37.90	$37.90
Purchase #2	$130.25	9.136%	$142.1496	$142.15	$142.15	$142.10
Purchase #3	$159.28	3.859%	$165.4266	$165.43	$165.45	$165.40
Purchase #4	$242.85	13.215%	$274.9426	$274.94	$274.95	$274.90
Purchase #5	$158.90	7.747%	$171.21	$171.21	$171.20	$171.20
Purchase #6	$221.33	10.643%	$244.8862	$244.89	$244.90	$244.90
Purchase #7	$176.41	9.548%	$193.2536	$193.25	$193.25	$193.30
7 purchase totals =	$1,122.39		$1,229.7569	$1,229.76	$1,229.80	$1,229.70