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	$241.38	3.599%	$250.0673	$250.07	$250.05	$250.10
Purchase #2	$94.79	8.498%	$102.8453	$102.85	$102.85	$102.80
Purchase #3	$138.91	11.453%	$154.8194	$154.82	$154.80	$154.80
Purchase #4	$95.81	4.405%	$100.0304	$100.03	$100.05	$100.00
Purchase #5	$24.50	4.183%	$25.5248	$25.52	$25.50	$25.50
Purchase #6	$174.92	13.360%	$198.2893	$198.29	$198.30	$198.30
Purchase #7	$213.40	4.834%	$223.7158	$223.72	$223.70	$223.70
7 purchase totals =	$983.71		$1,055.2923	$1,055.30	$1,055.25	$1,055.20