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	$38.39	11.649%	$42.8621	$42.86	$42.85	$42.90
Purchase #2	$155.26	9.397%	$169.8498	$169.85	$169.85	$169.80
Purchase #3	$148.34	11.358%	$165.1885	$165.19	$165.20	$165.20
Purchase #4	$227.35	4.802%	$238.2673	$238.27	$238.25	$238.30
Purchase #5	$42.58	9.638%	$46.6839	$46.68	$46.70	$46.70
Purchase #6	$197.59	12.449%	$222.188	$222.19	$222.20	$222.20
Purchase #7	$78.36	9.104%	$85.4939	$85.49	$85.50	$85.50
7 purchase totals =	$887.87		$970.5335	$970.53	$970.55	$970.60