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	$102.50	12.478%	$115.29	$115.29	$115.30	$115.30
Purchase #2	$207.55	13.388%	$235.3368	$235.34	$235.35	$235.30
Purchase #3	$9.90	7.298%	$10.6225	$10.62	$10.60	$10.60
Purchase #4	$164.43	11.570%	$183.4546	$183.45	$183.45	$183.50
Purchase #5	$55.27	8.293%	$59.8535	$59.85	$59.85	$59.90
Purchase #6	$238.27	9.386%	$260.634	$260.63	$260.65	$260.60
Purchase #7	$219.48	9.508%	$240.3482	$240.35	$240.35	$240.30
7 purchase totals =	$997.40		$1,105.5396	$1,105.53	$1,105.55	$1,105.50