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	$134.46	12.622%	$151.4315	$151.43	$151.45	$151.40
Purchase #2	$247.58	4.162%	$257.8843	$257.88	$257.90	$257.90
Purchase #3	$133.43	6.341%	$141.8908	$141.89	$141.90	$141.90
Purchase #4	$156.81	5.752%	$165.8297	$165.83	$165.85	$165.80
Purchase #5	$131.60	13.805%	$149.7674	$149.77	$149.75	$149.80
Purchase #6	$171.91	4.188%	$179.1096	$179.11	$179.10	$179.10
Purchase #7	$33.76	12.460%	$37.9665	$37.97	$37.95	$38.00
7 purchase totals =	$1,009.55		$1,083.8798	$1,083.88	$1,083.90	$1,083.90