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	$35.37	12.808%	$39.9002	$39.90	$39.90	$39.90
Purchase #2	$46.79	6.471%	$49.8178	$49.82	$49.80	$49.80
Purchase #3	$57.27	3.537%	$59.2956	$59.30	$59.30	$59.30
Purchase #4	$183.27	12.447%	$206.0816	$206.08	$206.10	$206.10
Purchase #5	$97.33	8.476%	$105.5797	$105.58	$105.60	$105.60
Purchase #6	$22.92	10.807%	$25.397	$25.40	$25.40	$25.40
Purchase #7	$245.88	12.408%	$276.3888	$276.39	$276.40	$276.40
7 purchase totals =	$688.83		$762.4607	$762.47	$762.50	$762.50