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	$78.84	13.860%	$89.7672	$89.77	$89.75	$89.80
Purchase #2	$124.70	6.253%	$132.4975	$132.50	$132.50	$132.50
Purchase #3	$209.71	10.271%	$231.2493	$231.25	$231.25	$231.20
Purchase #4	$123.67	12.615%	$139.271	$139.27	$139.25	$139.30
Purchase #5	$186.31	12.291%	$209.2094	$209.21	$209.20	$209.20
Purchase #6	$120.39	8.511%	$130.6364	$130.64	$130.65	$130.60
Purchase #7	$204.82	3.657%	$212.3103	$212.31	$212.30	$212.30
7 purchase totals =	$1,048.44		$1,144.9411	$1,144.95	$1,144.90	$1,144.90