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	$105.94	8.459%	$114.9015	$114.90	$114.90	$114.90
Purchase #2	$24.78	10.545%	$27.3931	$27.39	$27.40	$27.40
Purchase #3	$100.70	4.769%	$105.5024	$105.50	$105.50	$105.50
Purchase #4	$170.56	5.402%	$179.7737	$179.77	$179.75	$179.80
Purchase #5	$234.48	10.383%	$258.8261	$258.83	$258.85	$258.80
Purchase #6	$230.63	12.398%	$259.2235	$259.22	$259.20	$259.20
Purchase #7	$123.67	12.134%	$138.6761	$138.68	$138.70	$138.70
7 purchase totals =	$990.76		$1,084.2964	$1,084.29	$1,084.30	$1,084.30