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	$120.93	13.119%	$136.7948	$136.79	$136.80	$136.80
Purchase #2	$56.25	11.817%	$62.8971	$62.90	$62.90	$62.90
Purchase #3	$192.62	9.284%	$210.5028	$210.50	$210.50	$210.50
Purchase #4	$196.98	10.524%	$217.7102	$217.71	$217.70	$217.70
Purchase #5	$237.43	10.477%	$262.3055	$262.31	$262.30	$262.30
Purchase #6	$165.97	11.103%	$184.3976	$184.40	$184.40	$184.40
Purchase #7	$95.80	10.566%	$105.9222	$105.92	$105.90	$105.90
7 purchase totals =	$1,065.98		$1,180.5302	$1,180.53	$1,180.50	$1,180.50