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	$109.31	5.792%	$115.6412	$115.64	$115.65	$115.60
Purchase #2	$175.80	11.744%	$196.446	$196.45	$196.45	$196.40
Purchase #3	$104.48	7.650%	$112.4727	$112.47	$112.45	$112.50
Purchase #4	$207.54	11.473%	$231.3511	$231.35	$231.35	$231.40
Purchase #5	$13.80	13.671%	$15.6866	$15.69	$15.70	$15.70
Purchase #6	$196.39	9.425%	$214.8998	$214.90	$214.90	$214.90
Purchase #7	$70.70	11.506%	$78.8347	$78.83	$78.85	$78.80
7 purchase totals =	$878.02		$965.3321	$965.33	$965.35	$965.30