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	$54.50	4.108%	$56.7389	$56.74	$56.75	$56.70
Purchase #2	$114.65	5.412%	$120.8549	$120.85	$120.85	$120.90
Purchase #3	$137.59	9.551%	$150.7312	$150.73	$150.75	$150.70
Purchase #4	$74.76	10.708%	$82.7653	$82.77	$82.75	$82.80
Purchase #5	$152.85	12.466%	$171.9043	$171.90	$171.90	$171.90
Purchase #6	$126.72	5.587%	$133.7998	$133.80	$133.80	$133.80
Purchase #7	$88.81	3.372%	$91.8047	$91.80	$91.80	$91.80
7 purchase totals =	$749.88		$808.5991	$808.59	$808.60	$808.60