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	$73.94	13.432%	$83.8716	$83.87	$83.85	$83.90
Purchase #2	$93.29	6.171%	$99.0469	$99.05	$99.05	$99.00
Purchase #3	$155.74	4.776%	$163.1781	$163.18	$163.20	$163.20
Purchase #4	$116.87	9.167%	$127.5835	$127.58	$127.60	$127.60
Purchase #5	$65.89	10.511%	$72.8157	$72.82	$72.80	$72.80
Purchase #6	$206.48	8.426%	$223.878	$223.88	$223.90	$223.90
Purchase #7	$227.91	9.416%	$249.37	$249.37	$249.35	$249.40
7 purchase totals =	$940.12		$1,019.7438	$1,019.75	$1,019.75	$1,019.80