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	$67.70	6.286%	$71.9556	$71.96	$71.95	$72.00
Purchase #2	$171.58	4.850%	$179.9016	$179.90	$179.90	$179.90
Purchase #3	$216.50	11.824%	$242.099	$242.10	$242.10	$242.10
Purchase #4	$168.37	12.544%	$189.4903	$189.49	$189.50	$189.50
Purchase #5	$103.68	7.252%	$111.1989	$111.20	$111.20	$111.20
Purchase #6	$106.81	6.208%	$113.4408	$113.44	$113.45	$113.40
Purchase #7	$19.67	5.535%	$20.7587	$20.76	$20.75	$20.80
7 purchase totals =	$854.31		$928.8449	$928.85	$928.85	$928.90