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	$101.75	7.572%	$109.4545	$109.45	$109.45	$109.50
Purchase #2	$171.84	11.633%	$191.8301	$191.83	$191.85	$191.80
Purchase #3	$94.33	8.209%	$102.0735	$102.07	$102.05	$102.10
Purchase #4	$169.48	10.851%	$187.8703	$187.87	$187.85	$187.90
Purchase #5	$118.55	10.510%	$131.0096	$131.01	$131.00	$131.00
Purchase #6	$20.37	7.784%	$21.9556	$21.96	$21.95	$22.00
Purchase #7	$139.49	12.337%	$156.6989	$156.70	$156.70	$156.70
7 purchase totals =	$815.81		$900.8925	$900.89	$900.85	$901.00