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	$213.49	12.696%	$240.5947	$240.59	$240.60	$240.60
Purchase #2	$189.89	5.363%	$200.0738	$200.07	$200.05	$200.10
Purchase #3	$128.52	12.216%	$144.22	$144.22	$144.20	$144.20
Purchase #4	$192.90	11.781%	$215.6255	$215.63	$215.65	$215.60
Purchase #5	$103.29	13.113%	$116.8344	$116.83	$116.85	$116.80
Purchase #6	$47.45	3.734%	$49.2218	$49.22	$49.20	$49.20
Purchase #7	$175.32	3.764%	$181.919	$181.92	$181.90	$181.90
7 purchase totals =	$1,050.86		$1,148.4892	$1,148.48	$1,148.45	$1,148.40