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	$54.81	3.743%	$56.8615	$56.86	$56.85	$56.90
Purchase #2	$46.32	12.540%	$52.1285	$52.13	$52.15	$52.10
Purchase #3	$25.85	6.610%	$27.5587	$27.56	$27.55	$27.60
Purchase #4	$160.34	13.231%	$181.5546	$181.55	$181.55	$181.60
Purchase #5	$123.61	11.602%	$137.9512	$137.95	$137.95	$138.00
Purchase #6	$165.90	3.134%	$171.0993	$171.10	$171.10	$171.10
Purchase #7	$158.25	6.654%	$168.78	$168.78	$168.80	$168.80
7 purchase totals =	$735.08		$795.9338	$795.93	$795.95	$796.10