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	$65.43	8.321%	$70.8744	$70.87	$70.85	$70.90
Purchase #2	$33.77	4.442%	$35.2701	$35.27	$35.25	$35.30
Purchase #3	$31.61	7.741%	$34.0569	$34.06	$34.05	$34.10
Purchase #4	$38.31	11.181%	$42.5934	$42.59	$42.60	$42.60
Purchase #5	$137.29	12.649%	$154.6558	$154.66	$154.65	$154.70
Purchase #6	$160.80	4.421%	$167.909	$167.91	$167.90	$167.90
Purchase #7	$27.50	11.157%	$30.5682	$30.57	$30.55	$30.60
7 purchase totals =	$494.71		$535.9278	$535.93	$535.85	$536.10