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	$167.90	11.495%	$187.2001	$187.20	$187.20	$187.20
Purchase #2	$94.59	5.416%	$99.713	$99.71	$99.70	$99.70
Purchase #3	$164.59	8.671%	$178.8616	$178.86	$178.85	$178.90
Purchase #4	$180.38	5.394%	$190.1097	$190.11	$190.10	$190.10
Purchase #5	$193.85	8.296%	$209.9318	$209.93	$209.95	$209.90
Purchase #6	$99.81	11.239%	$111.0276	$111.03	$111.05	$111.00
Purchase #7	$86.35	13.628%	$98.1178	$98.12	$98.10	$98.10
7 purchase totals =	$987.47		$1,074.9616	$1,074.96	$1,074.95	$1,074.90