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	$163.43	4.450%	$170.7026	$170.70	$170.70	$170.70
Purchase #2	$78.83	4.290%	$82.2118	$82.21	$82.20	$82.20
Purchase #3	$68.57	4.521%	$71.67	$71.67	$71.65	$71.70
Purchase #4	$93.30	9.684%	$102.3352	$102.34	$102.35	$102.30
Purchase #5	$107.98	3.462%	$111.7183	$111.72	$111.70	$111.70
Purchase #6	$47.48	7.752%	$51.1606	$51.16	$51.15	$51.20
Purchase #7	$226.83	10.166%	$249.8895	$249.89	$249.90	$249.90
7 purchase totals =	$786.42		$839.6880	$839.69	$839.65	$839.70