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	$120.88	13.861%	$137.6352	$137.64	$137.65	$137.60
Purchase #2	$163.55	9.476%	$179.048	$179.05	$179.05	$179.00
Purchase #3	$196.33	10.729%	$217.3942	$217.39	$217.40	$217.40
Purchase #4	$36.37	12.245%	$40.8235	$40.82	$40.80	$40.80
Purchase #5	$69.81	13.115%	$78.9656	$78.97	$78.95	$79.00
Purchase #6	$80.46	12.138%	$90.2262	$90.23	$90.25	$90.20
Purchase #7	$204.35	4.829%	$214.2181	$214.22	$214.20	$214.20
7 purchase totals =	$871.75		$958.3108	$958.32	$958.30	$958.20