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	$135.52	12.450%	$152.3922	$152.39	$152.40	$152.40
Purchase #2	$33.90	10.443%	$37.4402	$37.44	$37.45	$37.40
Purchase #3	$202.54	7.356%	$217.4388	$217.44	$217.45	$217.40
Purchase #4	$105.37	10.837%	$116.7889	$116.79	$116.80	$116.80
Purchase #5	$81.40	5.235%	$85.6613	$85.66	$85.65	$85.70
Purchase #6	$174.71	5.213%	$183.8176	$183.82	$183.80	$183.80
Purchase #7	$82.25	9.866%	$90.3648	$90.36	$90.35	$90.40
7 purchase totals =	$815.69		$883.9038	$883.90	$883.90	$883.90