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	$52.60	5.587%	$55.5388	$55.54	$55.55	$55.50
Purchase #2	$221.93	13.241%	$251.3158	$251.32	$251.30	$251.30
Purchase #3	$196.84	10.212%	$216.9413	$216.94	$216.95	$216.90
Purchase #4	$115.83	7.302%	$124.2879	$124.29	$124.30	$124.30
Purchase #5	$122.68	6.823%	$131.0505	$131.05	$131.05	$131.10
Purchase #6	$102.73	4.628%	$107.4843	$107.48	$107.50	$107.50
Purchase #7	$109.81	6.371%	$116.806	$116.81	$116.80	$116.80
7 purchase totals =	$922.42		$1,003.4246	$1,003.43	$1,003.45	$1,003.40