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	$28.40	10.360%	$31.3422	$31.34	$31.35	$31.30
Purchase #2	$37.80	4.143%	$39.3661	$39.37	$39.35	$39.40
Purchase #3	$207.72	7.269%	$222.8192	$222.82	$222.80	$222.80
Purchase #4	$58.94	10.749%	$65.2755	$65.28	$65.30	$65.30
Purchase #5	$181.34	4.404%	$189.3262	$189.33	$189.35	$189.30
Purchase #6	$103.82	13.139%	$117.4609	$117.46	$117.45	$117.50
Purchase #7	$152.48	6.189%	$161.917	$161.92	$161.90	$161.90
7 purchase totals =	$770.50		$827.5071	$827.52	$827.50	$827.50