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	$142.60	7.150%	$152.7959	$152.80	$152.80	$152.80
Purchase #2	$109.71	4.540%	$114.6908	$114.69	$114.70	$114.70
Purchase #3	$64.37	12.645%	$72.5096	$72.51	$72.50	$72.50
Purchase #4	$65.46	9.322%	$71.5622	$71.56	$71.55	$71.60
Purchase #5	$210.31	12.455%	$236.5041	$236.50	$236.50	$236.50
Purchase #6	$52.52	7.622%	$56.5231	$56.52	$56.50	$56.50
Purchase #7	$198.69	11.771%	$222.0778	$222.08	$222.10	$222.10
7 purchase totals =	$843.66		$926.6635	$926.66	$926.65	$926.70