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	$99.84	3.761%	$103.595	$103.60	$103.60	$103.60
Purchase #2	$50.92	11.273%	$56.6602	$56.66	$56.65	$56.70
Purchase #3	$90.98	11.869%	$101.7784	$101.78	$101.80	$101.80
Purchase #4	$63.88	13.436%	$72.4629	$72.46	$72.45	$72.50
Purchase #5	$160.55	8.455%	$174.1245	$174.12	$174.10	$174.10
Purchase #6	$38.82	4.650%	$40.6251	$40.63	$40.65	$40.60
Purchase #7	$61.56	3.299%	$63.5909	$63.59	$63.60	$63.60
7 purchase totals =	$566.55		$612.8370	$612.84	$612.85	$612.90