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	$187.76	12.324%	$210.8995	$210.90	$210.90	$210.90
Purchase #2	$153.25	9.868%	$168.3727	$168.37	$168.35	$168.40
Purchase #3	$241.60	5.496%	$254.8783	$254.88	$254.90	$254.90
Purchase #4	$168.50	8.385%	$182.6287	$182.63	$182.65	$182.60
Purchase #5	$106.85	6.240%	$113.5174	$113.52	$113.50	$113.50
Purchase #6	$168.39	10.695%	$186.3993	$186.40	$186.40	$186.40
Purchase #7	$74.30	11.294%	$82.6914	$82.69	$82.70	$82.70
7 purchase totals =	$1,100.65		$1,199.3873	$1,199.39	$1,199.40	$1,199.40