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	$82.99	3.353%	$85.7727	$85.77	$85.75	$85.80
Purchase #2	$81.44	6.701%	$86.8973	$86.90	$86.90	$86.90
Purchase #3	$51.29	10.856%	$56.858	$56.86	$56.85	$56.90
Purchase #4	$146.89	3.692%	$152.3132	$152.31	$152.30	$152.30
Purchase #5	$94.81	3.630%	$98.2516	$98.25	$98.25	$98.30
Purchase #6	$170.56	12.308%	$191.5525	$191.55	$191.55	$191.60
Purchase #7	$127.99	7.669%	$137.8056	$137.81	$137.80	$137.80
7 purchase totals =	$755.97		$809.4509	$809.45	$809.40	$809.60