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	$166.74	7.233%	$178.8003	$178.80	$178.80	$178.80
Purchase #2	$206.64	3.241%	$213.3372	$213.34	$213.35	$213.30
Purchase #3	$86.82	6.654%	$92.597	$92.60	$92.60	$92.60
Purchase #4	$138.79	11.751%	$155.0992	$155.10	$155.10	$155.10
Purchase #5	$22.59	13.352%	$25.6062	$25.61	$25.60	$25.60
Purchase #6	$83.48	8.212%	$90.3354	$90.34	$90.35	$90.30
Purchase #7	$52.43	13.821%	$59.6764	$59.68	$59.70	$59.70
7 purchase totals =	$757.49		$815.4517	$815.47	$815.50	$815.40