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	$76.86	4.287%	$80.155	$80.16	$80.15	$80.20
Purchase #2	$84.72	10.522%	$93.6342	$93.63	$93.65	$93.60
Purchase #3	$157.70	4.559%	$164.8895	$164.89	$164.90	$164.90
Purchase #4	$59.55	4.466%	$62.2095	$62.21	$62.20	$62.20
Purchase #5	$143.87	4.725%	$150.6679	$150.67	$150.65	$150.70
Purchase #6	$88.25	4.798%	$92.4842	$92.48	$92.50	$92.50
Purchase #7	$124.44	3.524%	$128.8253	$128.83	$128.85	$128.80
7 purchase totals =	$735.39		$772.8656	$772.87	$772.90	$772.90