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	$137.39	10.136%	$151.3159	$151.32	$151.30	$151.30
Purchase #2	$94.61	9.546%	$103.6415	$103.64	$103.65	$103.60
Purchase #3	$50.44	6.481%	$53.709	$53.71	$53.70	$53.70
Purchase #4	$84.60	3.375%	$87.4553	$87.46	$87.45	$87.50
Purchase #5	$119.83	12.516%	$134.8279	$134.83	$134.85	$134.80
Purchase #6	$202.43	6.821%	$216.2378	$216.24	$216.25	$216.20
Purchase #7	$50.35	13.443%	$57.1186	$57.12	$57.10	$57.10
7 purchase totals =	$739.65		$804.3060	$804.32	$804.30	$804.20