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	$249.49	3.363%	$257.8803	$257.88	$257.90	$257.90
Purchase #2	$205.78	5.257%	$216.5979	$216.60	$216.60	$216.60
Purchase #3	$72.93	4.735%	$76.3832	$76.38	$76.40	$76.40
Purchase #4	$202.49	11.548%	$225.8735	$225.87	$225.85	$225.90
Purchase #5	$250.77	3.260%	$258.9451	$258.95	$258.95	$258.90
Purchase #6	$37.85	7.161%	$40.5604	$40.56	$40.55	$40.60
Purchase #7	$39.70	3.118%	$40.9378	$40.94	$40.95	$40.90
7 purchase totals =	$1,059.01		$1,117.1782	$1,117.18	$1,117.20	$1,117.20