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	$200.34	3.119%	$206.5886	$206.59	$206.60	$206.60
Purchase #2	$40.85	6.454%	$43.4865	$43.49	$43.50	$43.50
Purchase #3	$120.33	7.131%	$128.9107	$128.91	$128.90	$128.90
Purchase #4	$49.82	11.201%	$55.4003	$55.40	$55.40	$55.40
Purchase #5	$140.40	4.439%	$146.6324	$146.63	$146.65	$146.60
Purchase #6	$169.93	7.715%	$183.0401	$183.04	$183.05	$183.00
Purchase #7	$208.70	6.118%	$221.4683	$221.47	$221.45	$221.50
7 purchase totals =	$930.37		$985.5269	$985.53	$985.55	$985.50