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	$96.97	7.580%	$104.3203	$104.32	$104.30	$104.30
Purchase #2	$85.89	3.620%	$88.9992	$89.00	$89.00	$89.00
Purchase #3	$105.32	3.147%	$108.6344	$108.63	$108.65	$108.60
Purchase #4	$6.42	10.413%	$7.0885	$7.09	$7.10	$7.10
Purchase #5	$207.73	7.191%	$222.6679	$222.67	$222.65	$222.70
Purchase #6	$249.25	10.257%	$274.8156	$274.82	$274.80	$274.80
Purchase #7	$61.48	6.225%	$65.3071	$65.31	$65.30	$65.30
7 purchase totals =	$813.06		$871.8330	$871.84	$871.80	$871.80