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	$101.78	11.549%	$113.5346	$113.53	$113.55	$113.50
Purchase #2	$90.34	11.264%	$100.5159	$100.52	$100.50	$100.50
Purchase #3	$233.55	4.736%	$244.6109	$244.61	$244.60	$244.60
Purchase #4	$85.50	9.874%	$93.9423	$93.94	$93.95	$93.90
Purchase #5	$52.52	7.803%	$56.6181	$56.62	$56.60	$56.60
Purchase #6	$51.53	10.749%	$57.069	$57.07	$57.05	$57.10
Purchase #7	$161.39	9.842%	$177.274	$177.27	$177.25	$177.30
7 purchase totals =	$776.61		$843.5648	$843.56	$843.50	$843.50