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	$81.58	10.145%	$89.8563	$89.86	$89.85	$89.90
Purchase #2	$59.32	8.803%	$64.5419	$64.54	$64.55	$64.50
Purchase #3	$89.90	3.376%	$92.935	$92.94	$92.95	$92.90
Purchase #4	$20.84	8.235%	$22.5562	$22.56	$22.55	$22.60
Purchase #5	$148.84	9.186%	$162.5124	$162.51	$162.50	$162.50
Purchase #6	$154.98	3.507%	$160.4151	$160.42	$160.40	$160.40
Purchase #7	$12.64	6.313%	$13.438	$13.44	$13.45	$13.40
7 purchase totals =	$568.10		$606.2549	$606.27	$606.25	$606.20