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	$29.35	5.732%	$31.0323	$31.03	$31.05	$31.00
Purchase #2	$143.59	4.671%	$150.2971	$150.30	$150.30	$150.30
Purchase #3	$31.66	4.324%	$33.029	$33.03	$33.05	$33.00
Purchase #4	$96.39	6.527%	$102.6814	$102.68	$102.70	$102.70
Purchase #5	$35.69	6.745%	$38.0973	$38.10	$38.10	$38.10
Purchase #6	$90.62	8.566%	$98.3825	$98.38	$98.40	$98.40
Purchase #7	$54.83	11.803%	$61.3016	$61.30	$61.30	$61.30
7 purchase totals =	$482.13		$514.8212	$514.82	$514.90	$514.80