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	$59.91	7.817%	$64.5932	$64.59	$64.60	$64.60
Purchase #2	$63.73	5.249%	$67.0752	$67.08	$67.10	$67.10
Purchase #3	$112.48	12.575%	$126.6244	$126.62	$126.60	$126.60
Purchase #4	$172.46	10.706%	$190.9236	$190.92	$190.90	$190.90
Purchase #5	$227.93	8.819%	$248.0311	$248.03	$248.05	$248.00
Purchase #6	$38.51	9.821%	$42.2921	$42.29	$42.30	$42.30
Purchase #7	$242.55	11.141%	$269.5725	$269.57	$269.55	$269.60
7 purchase totals =	$917.57		$1,009.1121	$1,009.10	$1,009.10	$1,009.10