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	$131.42	5.410%	$138.5298	$138.53	$138.55	$138.50
Purchase #2	$233.86	4.310%	$243.9394	$243.94	$243.95	$243.90
Purchase #3	$19.27	12.274%	$21.6352	$21.64	$21.65	$21.60
Purchase #4	$230.27	6.687%	$245.6682	$245.67	$245.65	$245.70
Purchase #5	$240.33	6.397%	$255.7039	$255.70	$255.70	$255.70
Purchase #6	$137.86	3.233%	$142.317	$142.32	$142.30	$142.30
Purchase #7	$40.93	3.490%	$42.3585	$42.36	$42.35	$42.40
7 purchase totals =	$1,033.94		$1,090.1520	$1,090.16	$1,090.15	$1,090.10