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	$73.72	9.387%	$80.6401	$80.64	$80.65	$80.60
Purchase #2	$178.80	6.762%	$190.8905	$190.89	$190.90	$190.90
Purchase #3	$46.96	6.789%	$50.1481	$50.15	$50.15	$50.10
Purchase #4	$60.92	5.675%	$64.3772	$64.38	$64.40	$64.40
Purchase #5	$57.82	13.237%	$65.4736	$65.47	$65.45	$65.50
Purchase #6	$110.50	3.430%	$114.2902	$114.29	$114.30	$114.30
Purchase #7	$126.31	12.688%	$142.3362	$142.34	$142.35	$142.30
7 purchase totals =	$655.03		$708.1559	$708.16	$708.20	$708.10