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	$36.31	9.850%	$39.8865	$39.89	$39.90	$39.90
Purchase #2	$168.39	5.706%	$177.9983	$178.00	$178.00	$178.00
Purchase #3	$105.61	13.184%	$119.5336	$119.53	$119.55	$119.50
Purchase #4	$130.96	7.359%	$140.5973	$140.60	$140.60	$140.60
Purchase #5	$28.87	13.789%	$32.8509	$32.85	$32.85	$32.90
Purchase #6	$234.35	4.485%	$244.8606	$244.86	$244.85	$244.90
Purchase #7	$6.94	8.834%	$7.5531	$7.55	$7.55	$7.60
7 purchase totals =	$711.43		$763.2803	$763.28	$763.30	$763.40