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	$62.45	13.517%	$70.8914	$70.89	$70.90	$70.90
Purchase #2	$149.43	5.190%	$157.1854	$157.19	$157.20	$157.20
Purchase #3	$134.78	8.416%	$146.1231	$146.12	$146.10	$146.10
Purchase #4	$120.52	11.447%	$134.3159	$134.32	$134.30	$134.30
Purchase #5	$223.58	7.681%	$240.7532	$240.75	$240.75	$240.80
Purchase #6	$89.81	6.690%	$95.8183	$95.82	$95.80	$95.80
Purchase #7	$176.92	11.319%	$196.9456	$196.95	$196.95	$196.90
7 purchase totals =	$957.49		$1,042.0329	$1,042.04	$1,042.00	$1,042.00