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	$46.98	12.542%	$52.8722	$52.87	$52.85	$52.90
Purchase #2	$29.54	12.697%	$33.2907	$33.29	$33.30	$33.30
Purchase #3	$81.87	10.453%	$90.4279	$90.43	$90.45	$90.40
Purchase #4	$21.61	13.206%	$24.4638	$24.46	$24.45	$24.50
Purchase #5	$61.34	5.362%	$64.6291	$64.63	$64.65	$64.60
Purchase #6	$42.39	11.774%	$47.381	$47.38	$47.40	$47.40
Purchase #7	$178.35	8.149%	$192.8837	$192.88	$192.90	$192.90
7 purchase totals =	$462.08		$505.9484	$505.94	$506.00	$506.00