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	$248.66	12.184%	$278.9567	$278.96	$278.95	$279.00
Purchase #2	$55.59	13.718%	$63.2158	$63.22	$63.20	$63.20
Purchase #3	$249.30	4.222%	$259.8254	$259.83	$259.85	$259.80
Purchase #4	$30.56	6.382%	$32.5103	$32.51	$32.50	$32.50
Purchase #5	$141.95	11.687%	$158.5397	$158.54	$158.55	$158.50
Purchase #6	$196.70	7.529%	$211.5095	$211.51	$211.50	$211.50
Purchase #7	$70.58	12.705%	$79.5472	$79.55	$79.55	$79.50
7 purchase totals =	$993.34		$1,084.1046	$1,084.12	$1,084.10	$1,084.00