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	$131.82	9.713%	$144.6237	$144.62	$144.60	$144.60
Purchase #2	$30.92	7.434%	$33.2186	$33.22	$33.20	$33.20
Purchase #3	$128.99	10.654%	$142.7326	$142.73	$142.75	$142.70
Purchase #4	$55.59	13.210%	$62.9334	$62.93	$62.95	$62.90
Purchase #5	$98.95	13.510%	$112.3181	$112.32	$112.30	$112.30
Purchase #6	$204.99	3.307%	$211.769	$211.77	$211.75	$211.80
Purchase #7	$82.95	9.572%	$90.89	$90.89	$90.90	$90.90
7 purchase totals =	$734.21		$798.4854	$798.48	$798.45	$798.40