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	$86.92	3.453%	$89.9213	$89.92	$89.90	$89.90
Purchase #2	$157.96	12.602%	$177.8661	$177.87	$177.85	$177.90
Purchase #3	$75.37	3.535%	$78.0343	$78.03	$78.05	$78.00
Purchase #4	$167.43	9.276%	$182.9608	$182.96	$182.95	$183.00
Purchase #5	$41.30	9.669%	$45.2933	$45.29	$45.30	$45.30
Purchase #6	$32.51	6.191%	$34.5227	$34.52	$34.50	$34.50
Purchase #7	$125.93	12.654%	$141.8652	$141.87	$141.85	$141.90
7 purchase totals =	$687.42		$750.4637	$750.46	$750.40	$750.50