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	$52.39	13.667%	$59.5501	$59.55	$59.55	$59.60
Purchase #2	$146.90	12.166%	$164.7719	$164.77	$164.75	$164.80
Purchase #3	$138.29	4.721%	$144.8187	$144.82	$144.80	$144.80
Purchase #4	$244.35	11.756%	$273.0758	$273.08	$273.10	$273.10
Purchase #5	$87.99	11.231%	$97.8722	$97.87	$97.85	$97.90
Purchase #6	$191.69	3.838%	$199.0471	$199.05	$199.05	$199.00
Purchase #7	$33.45	13.539%	$37.9788	$37.98	$38.00	$38.00
7 purchase totals =	$895.06		$977.1146	$977.12	$977.10	$977.20