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	$213.50	3.464%	$220.8956	$220.90	$220.90	$220.90
Purchase #2	$34.53	11.107%	$38.3652	$38.37	$38.35	$38.40
Purchase #3	$103.72	9.619%	$113.6968	$113.70	$113.70	$113.70
Purchase #4	$154.55	13.401%	$175.2612	$175.26	$175.25	$175.30
Purchase #5	$135.68	13.418%	$153.8855	$153.89	$153.90	$153.90
Purchase #6	$122.81	3.820%	$127.5013	$127.50	$127.50	$127.50
Purchase #7	$59.59	3.856%	$61.8878	$61.89	$61.90	$61.90
7 purchase totals =	$824.38		$891.4934	$891.51	$891.50	$891.60