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	$56.47	5.378%	$59.507	$59.51	$59.50	$59.50
Purchase #2	$201.65	7.553%	$216.8806	$216.88	$216.90	$216.90
Purchase #3	$47.93	13.587%	$54.4422	$54.44	$54.45	$54.40
Purchase #4	$87.48	10.745%	$96.8797	$96.88	$96.90	$96.90
Purchase #5	$221.77	10.615%	$245.3109	$245.31	$245.30	$245.30
Purchase #6	$22.63	3.198%	$23.3537	$23.35	$23.35	$23.40
Purchase #7	$101.71	3.420%	$105.1885	$105.19	$105.20	$105.20
7 purchase totals =	$739.64		$801.5626	$801.56	$801.60	$801.60