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	$180.60	11.198%	$200.8236	$200.82	$200.80	$200.80
Purchase #2	$94.36	4.795%	$98.8846	$98.88	$98.90	$98.90
Purchase #3	$191.85	4.558%	$200.5945	$200.59	$200.60	$200.60
Purchase #4	$119.89	11.730%	$133.9531	$133.95	$133.95	$134.00
Purchase #5	$92.59	13.806%	$105.373	$105.37	$105.35	$105.40
Purchase #6	$34.83	3.474%	$36.04	$36.04	$36.05	$36.00
Purchase #7	$64.30	7.150%	$68.8975	$68.90	$68.90	$68.90
7 purchase totals =	$778.42		$844.5663	$844.55	$844.55	$844.60