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	$164.41	12.300%	$184.6324	$184.63	$184.65	$184.60
Purchase #2	$239.93	10.231%	$264.4772	$264.48	$264.50	$264.50
Purchase #3	$47.91	13.246%	$54.2562	$54.26	$54.25	$54.30
Purchase #4	$101.42	8.510%	$110.0508	$110.05	$110.05	$110.10
Purchase #5	$135.60	6.600%	$144.5496	$144.55	$144.55	$144.50
Purchase #6	$109.89	3.781%	$114.0449	$114.04	$114.05	$114.00
Purchase #7	$65.56	3.451%	$67.8225	$67.82	$67.80	$67.80
7 purchase totals =	$864.72		$939.8336	$939.83	$939.85	$939.80