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	$124.41	5.633%	$131.418	$131.42	$131.40	$131.40
Purchase #2	$150.25	4.311%	$156.7273	$156.73	$156.75	$156.70
Purchase #3	$94.98	5.579%	$100.2789	$100.28	$100.30	$100.30
Purchase #4	$56.35	8.151%	$60.9431	$60.94	$60.95	$60.90
Purchase #5	$236.67	7.709%	$254.9149	$254.91	$254.90	$254.90
Purchase #6	$39.38	10.737%	$43.6082	$43.61	$43.60	$43.60
Purchase #7	$45.52	10.530%	$50.3133	$50.31	$50.30	$50.30
7 purchase totals =	$747.56		$798.2037	$798.20	$798.20	$798.10