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	$90.38	10.804%	$100.1447	$100.14	$100.15	$100.10
Purchase #2	$204.91	5.267%	$215.7026	$215.70	$215.70	$215.70
Purchase #3	$83.98	12.207%	$94.2314	$94.23	$94.25	$94.20
Purchase #4	$225.90	6.307%	$240.1475	$240.15	$240.15	$240.10
Purchase #5	$87.43	4.130%	$91.0409	$91.04	$91.05	$91.00
Purchase #6	$29.78	10.411%	$32.8804	$32.88	$32.90	$32.90
Purchase #7	$182.65	9.632%	$200.2428	$200.24	$200.25	$200.20
7 purchase totals =	$905.03		$974.3903	$974.38	$974.45	$974.20