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	$141.40	3.129%	$145.8244	$145.82	$145.80	$145.80
Purchase #2	$175.69	11.743%	$196.3213	$196.32	$196.30	$196.30
Purchase #3	$145.56	10.185%	$160.3853	$160.39	$160.40	$160.40
Purchase #4	$211.65	4.152%	$220.4377	$220.44	$220.45	$220.40
Purchase #5	$22.45	9.815%	$24.6535	$24.65	$24.65	$24.70
Purchase #6	$166.93	4.455%	$174.3667	$174.37	$174.35	$174.40
Purchase #7	$101.93	7.763%	$109.8428	$109.84	$109.85	$109.80
7 purchase totals =	$965.61		$1,031.8317	$1,031.83	$1,031.80	$1,031.80