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	$31.88	5.482%	$33.6277	$33.63	$33.65	$33.60
Purchase #2	$166.63	13.140%	$188.5252	$188.53	$188.55	$188.50
Purchase #3	$116.52	12.584%	$131.1829	$131.18	$131.20	$131.20
Purchase #4	$218.25	12.466%	$245.457	$245.46	$245.45	$245.50
Purchase #5	$121.68	6.116%	$129.1219	$129.12	$129.10	$129.10
Purchase #6	$123.27	13.394%	$139.7808	$139.78	$139.80	$139.80
Purchase #7	$44.54	11.370%	$49.6042	$49.60	$49.60	$49.60
7 purchase totals =	$822.77		$917.2997	$917.30	$917.35	$917.30