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	$173.50	3.772%	$180.0444	$180.04	$180.05	$180.00
Purchase #2	$128.55	6.329%	$136.6859	$136.69	$136.70	$136.70
Purchase #3	$211.69	7.304%	$227.1518	$227.15	$227.15	$227.20
Purchase #4	$232.32	3.227%	$239.817	$239.82	$239.80	$239.80
Purchase #5	$240.54	7.194%	$257.8444	$257.84	$257.85	$257.80
Purchase #6	$116.38	9.508%	$127.4454	$127.45	$127.45	$127.40
Purchase #7	$78.62	8.738%	$85.4898	$85.49	$85.50	$85.50
7 purchase totals =	$1,181.60		$1,254.4787	$1,254.48	$1,254.50	$1,254.40