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	$72.25	13.339%	$81.8874	$81.89	$81.90	$81.90
Purchase #2	$54.55	5.653%	$57.6337	$57.63	$57.65	$57.60
Purchase #3	$227.74	9.111%	$248.4894	$248.49	$248.50	$248.50
Purchase #4	$109.62	12.393%	$123.2052	$123.21	$123.20	$123.20
Purchase #5	$126.47	11.217%	$140.6561	$140.66	$140.65	$140.70
Purchase #6	$51.67	9.472%	$56.5642	$56.56	$56.55	$56.60
Purchase #7	$25.42	8.581%	$27.6013	$27.60	$27.60	$27.60
7 purchase totals =	$667.72		$736.0373	$736.04	$736.05	$736.10