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	$123.30	6.551%	$131.3774	$131.38	$131.40	$131.40
Purchase #2	$123.56	12.682%	$139.2299	$139.23	$139.25	$139.20
Purchase #3	$199.28	13.339%	$225.862	$225.86	$225.85	$225.90
Purchase #4	$48.55	10.837%	$53.8114	$53.81	$53.80	$53.80
Purchase #5	$203.90	7.229%	$218.6399	$218.64	$218.65	$218.60
Purchase #6	$227.93	9.259%	$249.034	$249.03	$249.05	$249.00
Purchase #7	$179.95	13.329%	$203.9355	$203.94	$203.95	$203.90
7 purchase totals =	$1,106.47		$1,221.8901	$1,221.89	$1,221.95	$1,221.80