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	$182.38	3.350%	$188.4897	$188.49	$188.50	$188.50
Purchase #2	$41.44	10.747%	$45.8936	$45.89	$45.90	$45.90
Purchase #3	$148.82	6.683%	$158.7656	$158.77	$158.75	$158.80
Purchase #4	$189.67	3.355%	$196.0334	$196.03	$196.05	$196.00
Purchase #5	$45.52	9.321%	$49.7629	$49.76	$49.75	$49.80
Purchase #6	$144.94	3.829%	$150.4898	$150.49	$150.50	$150.50
Purchase #7	$155.30	7.660%	$167.196	$167.20	$167.20	$167.20
7 purchase totals =	$908.07		$956.6310	$956.63	$956.65	$956.70