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	$38.46	3.712%	$39.8876	$39.89	$39.90	$39.90
Purchase #2	$171.25	11.472%	$190.8958	$190.90	$190.90	$190.90
Purchase #3	$13.92	8.420%	$15.0921	$15.09	$15.10	$15.10
Purchase #4	$81.35	11.743%	$90.9029	$90.90	$90.90	$90.90
Purchase #5	$140.26	9.424%	$153.4781	$153.48	$153.50	$153.50
Purchase #6	$192.64	12.708%	$217.1207	$217.12	$217.10	$217.10
Purchase #7	$210.67	6.288%	$223.9169	$223.92	$223.90	$223.90
7 purchase totals =	$848.55		$931.2941	$931.30	$931.30	$931.30