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	$99.64	3.444%	$103.0716	$103.07	$103.05	$103.10
Purchase #2	$62.51	8.221%	$67.6489	$67.65	$67.65	$67.60
Purchase #3	$47.78	6.488%	$50.88	$50.88	$50.90	$50.90
Purchase #4	$105.45	10.448%	$116.4674	$116.47	$116.45	$116.50
Purchase #5	$40.46	3.762%	$41.9821	$41.98	$42.00	$42.00
Purchase #6	$196.34	8.372%	$212.7776	$212.78	$212.80	$212.80
Purchase #7	$30.90	13.750%	$35.1488	$35.15	$35.15	$35.10
7 purchase totals =	$583.08		$627.9764	$627.98	$628.00	$628.00