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	$221.75	10.435%	$244.8896	$244.89	$244.90	$244.90
Purchase #2	$137.72	9.214%	$150.4095	$150.41	$150.40	$150.40
Purchase #3	$74.63	10.345%	$82.3505	$82.35	$82.35	$82.40
Purchase #4	$29.89	6.387%	$31.7991	$31.80	$31.80	$31.80
Purchase #5	$52.44	3.835%	$54.4511	$54.45	$54.45	$54.50
Purchase #6	$49.79	11.517%	$55.5243	$55.52	$55.50	$55.50
Purchase #7	$178.83	11.352%	$199.1308	$199.13	$199.15	$199.10
7 purchase totals =	$745.05		$818.5549	$818.55	$818.55	$818.60