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	$149.74	10.586%	$165.5915	$165.59	$165.60	$165.60
Purchase #2	$114.25	12.296%	$128.2982	$128.30	$128.30	$128.30
Purchase #3	$169.91	5.710%	$179.6119	$179.61	$179.60	$179.60
Purchase #4	$37.96	6.797%	$40.5401	$40.54	$40.55	$40.50
Purchase #5	$234.32	8.824%	$254.9964	$255.00	$255.00	$255.00
Purchase #6	$109.58	10.635%	$121.2338	$121.23	$121.25	$121.20
Purchase #7	$232.49	5.218%	$244.6213	$244.62	$244.60	$244.60
7 purchase totals =	$1,048.25		$1,134.8932	$1,134.89	$1,134.90	$1,134.80