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	$91.89	6.760%	$98.1018	$98.10	$98.10	$98.10
Purchase #2	$71.32	12.313%	$80.1016	$80.10	$80.10	$80.10
Purchase #3	$29.58	8.754%	$32.1694	$32.17	$32.15	$32.20
Purchase #4	$151.33	10.588%	$167.3528	$167.35	$167.35	$167.40
Purchase #5	$137.37	5.256%	$144.5902	$144.59	$144.60	$144.60
Purchase #6	$83.95	10.618%	$92.8638	$92.86	$92.85	$92.90
Purchase #7	$32.55	6.447%	$34.6485	$34.65	$34.65	$34.60
7 purchase totals =	$597.99		$649.8281	$649.82	$649.80	$649.90