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	$126.29	3.758%	$131.036	$131.04	$131.05	$131.00
Purchase #2	$121.53	5.128%	$127.7621	$127.76	$127.75	$127.80
Purchase #3	$179.26	13.542%	$203.5354	$203.54	$203.55	$203.50
Purchase #4	$104.97	7.294%	$112.6265	$112.63	$112.65	$112.60
Purchase #5	$169.66	12.164%	$190.2974	$190.30	$190.30	$190.30
Purchase #6	$27.77	3.672%	$28.7897	$28.79	$28.80	$28.80
Purchase #7	$133.67	13.813%	$152.1338	$152.13	$152.15	$152.10
7 purchase totals =	$863.15		$946.1809	$946.19	$946.25	$946.10