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	$166.74	5.728%	$176.2909	$176.29	$176.30	$176.30
Purchase #2	$137.86	12.771%	$155.4661	$155.47	$155.45	$155.50
Purchase #3	$198.38	13.676%	$225.5104	$225.51	$225.50	$225.50
Purchase #4	$49.71	5.660%	$52.5236	$52.52	$52.50	$52.50
Purchase #5	$160.66	3.672%	$166.5594	$166.56	$166.55	$166.60
Purchase #6	$102.91	11.638%	$114.8867	$114.89	$114.90	$114.90
Purchase #7	$142.43	6.740%	$152.0298	$152.03	$152.05	$152.00
7 purchase totals =	$958.69		$1,043.2669	$1,043.27	$1,043.25	$1,043.30