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	$225.65	3.281%	$233.0536	$233.05	$233.05	$233.10
Purchase #2	$237.65	13.654%	$270.0987	$270.10	$270.10	$270.10
Purchase #3	$213.89	13.382%	$242.5128	$242.51	$242.50	$242.50
Purchase #4	$237.85	7.691%	$256.143	$256.14	$256.15	$256.10
Purchase #5	$175.50	8.436%	$190.3052	$190.31	$190.30	$190.30
Purchase #6	$250.28	7.776%	$269.7418	$269.74	$269.75	$269.70
Purchase #7	$163.86	10.175%	$180.5328	$180.53	$180.55	$180.50
7 purchase totals =	$1,504.68		$1,642.3879	$1,642.38	$1,642.40	$1,642.30