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	$101.38	11.244%	$112.7792	$112.78	$112.80	$112.80
Purchase #2	$28.57	6.425%	$30.4056	$30.41	$30.40	$30.40
Purchase #3	$109.26	11.296%	$121.602	$121.60	$121.60	$121.60
Purchase #4	$83.50	8.487%	$90.5866	$90.59	$90.60	$90.60
Purchase #5	$146.90	6.774%	$156.851	$156.85	$156.85	$156.90
Purchase #6	$71.74	9.268%	$78.3889	$78.39	$78.40	$78.40
Purchase #7	$50.80	8.491%	$55.1134	$55.11	$55.10	$55.10
7 purchase totals =	$592.15		$645.7267	$645.73	$645.75	$645.80