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	$102.33	7.309%	$109.8093	$109.81	$109.80	$109.80
Purchase #2	$10.82	7.216%	$11.6008	$11.60	$11.60	$11.60
Purchase #3	$227.50	4.152%	$236.9458	$236.95	$236.95	$236.90
Purchase #4	$18.86	5.417%	$19.8816	$19.88	$19.90	$19.90
Purchase #5	$232.46	7.755%	$250.4873	$250.49	$250.50	$250.50
Purchase #6	$79.98	13.286%	$90.6061	$90.61	$90.60	$90.60
Purchase #7	$17.97	8.362%	$19.4727	$19.47	$19.45	$19.50
7 purchase totals =	$689.92		$738.8036	$738.81	$738.80	$738.80