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	$49.50	6.305%	$52.621	$52.62	$52.60	$52.60
Purchase #2	$61.95	7.646%	$66.6867	$66.69	$66.70	$66.70
Purchase #3	$78.70	10.692%	$87.1146	$87.11	$87.10	$87.10
Purchase #4	$29.88	12.691%	$33.6721	$33.67	$33.65	$33.70
Purchase #5	$36.72	11.346%	$40.8863	$40.89	$40.90	$40.90
Purchase #6	$234.94	3.526%	$243.224	$243.22	$243.20	$243.20
Purchase #7	$33.68	10.499%	$37.2161	$37.22	$37.20	$37.20
7 purchase totals =	$525.37		$561.4208	$561.42	$561.35	$561.40