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	$66.49	6.638%	$70.9036	$70.90	$70.90	$70.90
Purchase #2	$72.75	8.226%	$78.7344	$78.73	$78.75	$78.70
Purchase #3	$181.81	9.275%	$198.6729	$198.67	$198.65	$198.70
Purchase #4	$93.88	10.700%	$103.9252	$103.93	$103.95	$103.90
Purchase #5	$90.78	10.516%	$100.3264	$100.33	$100.35	$100.30
Purchase #6	$194.25	6.473%	$206.8238	$206.82	$206.80	$206.80
Purchase #7	$11.71	5.464%	$12.3498	$12.35	$12.35	$12.30
7 purchase totals =	$711.67		$771.7361	$771.73	$771.75	$771.60