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	$249.25	10.244%	$274.7832	$274.78	$274.80	$274.80
Purchase #2	$74.64	5.676%	$78.8766	$78.88	$78.90	$78.90
Purchase #3	$240.50	7.827%	$259.3239	$259.32	$259.30	$259.30
Purchase #4	$205.49	8.600%	$223.1621	$223.16	$223.15	$223.20
Purchase #5	$106.78	9.272%	$116.6806	$116.68	$116.70	$116.70
Purchase #6	$171.43	3.124%	$176.7855	$176.79	$176.80	$176.80
Purchase #7	$107.78	4.793%	$112.9459	$112.95	$112.95	$112.90
7 purchase totals =	$1,155.87		$1,242.5578	$1,242.56	$1,242.60	$1,242.60