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	$34.56	5.664%	$36.5175	$36.52	$36.50	$36.50
Purchase #2	$65.61	10.377%	$72.4183	$72.42	$72.40	$72.40
Purchase #3	$159.59	3.157%	$164.6283	$164.63	$164.65	$164.60
Purchase #4	$236.40	12.233%	$265.3188	$265.32	$265.30	$265.30
Purchase #5	$10.66	12.609%	$12.0041	$12.00	$12.00	$12.00
Purchase #6	$245.55	11.738%	$274.3727	$274.37	$274.35	$274.40
Purchase #7	$129.96	6.453%	$138.3463	$138.35	$138.35	$138.30
7 purchase totals =	$882.33		$963.6060	$963.61	$963.55	$963.50