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	$139.94	9.181%	$152.7879	$152.79	$152.80	$152.80
Purchase #2	$30.31	5.369%	$31.9373	$31.94	$31.95	$31.90
Purchase #3	$109.55	3.739%	$113.6461	$113.65	$113.65	$113.60
Purchase #4	$159.61	4.404%	$166.6392	$166.64	$166.65	$166.60
Purchase #5	$110.54	10.493%	$122.139	$122.14	$122.15	$122.10
Purchase #6	$69.97	11.650%	$78.1215	$78.12	$78.10	$78.10
Purchase #7	$225.67	10.847%	$250.1484	$250.15	$250.15	$250.10
7 purchase totals =	$845.59		$915.4194	$915.43	$915.45	$915.20