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	$240.80	6.424%	$256.269	$256.27	$256.25	$256.30
Purchase #2	$82.35	3.859%	$85.5279	$85.53	$85.55	$85.50
Purchase #3	$75.35	8.600%	$81.8301	$81.83	$81.85	$81.80
Purchase #4	$36.77	4.206%	$38.3165	$38.32	$38.30	$38.30
Purchase #5	$37.28	8.424%	$40.4205	$40.42	$40.40	$40.40
Purchase #6	$65.62	9.850%	$72.0836	$72.08	$72.10	$72.10
Purchase #7	$202.63	8.778%	$220.4169	$220.42	$220.40	$220.40
7 purchase totals =	$740.80		$794.8645	$794.87	$794.85	$794.80