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	$68.90	4.788%	$72.1989	$72.20	$72.20	$72.20
Purchase #2	$141.99	12.128%	$159.2105	$159.21	$159.20	$159.20
Purchase #3	$127.39	11.829%	$142.459	$142.46	$142.45	$142.50
Purchase #4	$161.50	6.351%	$171.7569	$171.76	$171.75	$171.80
Purchase #5	$92.26	13.351%	$104.5776	$104.58	$104.60	$104.60
Purchase #6	$13.72	13.379%	$15.5556	$15.56	$15.55	$15.60
Purchase #7	$39.33	13.372%	$44.5892	$44.59	$44.60	$44.60
7 purchase totals =	$645.09		$710.3477	$710.36	$710.35	$710.50