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	$105.39	3.438%	$109.0133	$109.01	$109.00	$109.00
Purchase #2	$238.53	3.796%	$247.5846	$247.58	$247.60	$247.60
Purchase #3	$80.32	12.574%	$90.4194	$90.42	$90.40	$90.40
Purchase #4	$218.97	9.853%	$240.5451	$240.55	$240.55	$240.50
Purchase #5	$233.43	3.861%	$242.4427	$242.44	$242.45	$242.40
Purchase #6	$88.85	11.340%	$98.9256	$98.93	$98.95	$98.90
Purchase #7	$97.83	10.871%	$108.4651	$108.47	$108.45	$108.50
7 purchase totals =	$1,063.32		$1,137.3958	$1,137.40	$1,137.40	$1,137.30