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	$212.81	9.296%	$232.5928	$232.59	$232.60	$232.60
Purchase #2	$145.57	6.812%	$155.4862	$155.49	$155.50	$155.50
Purchase #3	$98.61	11.480%	$109.9304	$109.93	$109.95	$109.90
Purchase #4	$166.33	12.333%	$186.8435	$186.84	$186.85	$186.80
Purchase #5	$167.87	4.658%	$175.6894	$175.69	$175.70	$175.70
Purchase #6	$129.51	5.671%	$136.8545	$136.85	$136.85	$136.90
Purchase #7	$85.46	8.196%	$92.4643	$92.46	$92.45	$92.50
7 purchase totals =	$1,006.16		$1,089.8611	$1,089.85	$1,089.90	$1,089.90