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	$89.31	7.401%	$95.9198	$95.92	$95.90	$95.90
Purchase #2	$127.78	5.360%	$134.629	$134.63	$134.65	$134.60
Purchase #3	$51.88	12.115%	$58.1653	$58.17	$58.15	$58.20
Purchase #4	$90.27	12.184%	$101.2685	$101.27	$101.25	$101.30
Purchase #5	$65.55	6.620%	$69.8894	$69.89	$69.90	$69.90
Purchase #6	$113.45	11.481%	$126.4752	$126.48	$126.50	$126.50
Purchase #7	$82.58	13.293%	$93.5574	$93.56	$93.55	$93.60
7 purchase totals =	$620.82		$679.9046	$679.92	$679.90	$680.00