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	$33.63	6.714%	$35.8879	$35.89	$35.90	$35.90
Purchase #2	$188.87	13.642%	$214.6356	$214.64	$214.65	$214.60
Purchase #3	$52.59	13.477%	$59.6776	$59.68	$59.70	$59.70
Purchase #4	$57.79	11.775%	$64.5948	$64.59	$64.60	$64.60
Purchase #5	$196.58	10.764%	$217.7399	$217.74	$217.75	$217.70
Purchase #6	$68.39	7.442%	$73.4796	$73.48	$73.50	$73.50
Purchase #7	$5.83	10.726%	$6.4553	$6.46	$6.45	$6.50
7 purchase totals =	$603.68		$672.4707	$672.48	$672.55	$672.50