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	$71.64	12.416%	$80.5348	$80.53	$80.55	$80.50
Purchase #2	$45.80	11.507%	$51.0702	$51.07	$51.05	$51.10
Purchase #3	$195.61	5.241%	$205.8619	$205.86	$205.85	$205.90
Purchase #4	$231.59	12.222%	$259.8949	$259.89	$259.90	$259.90
Purchase #5	$172.82	7.400%	$185.6087	$185.61	$185.60	$185.60
Purchase #6	$37.46	4.746%	$39.2379	$39.24	$39.25	$39.20
Purchase #7	$152.65	3.570%	$158.0996	$158.10	$158.10	$158.10
7 purchase totals =	$907.57		$980.3080	$980.30	$980.30	$980.30