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	$93.62	6.766%	$99.9543	$99.95	$99.95	$100.00
Purchase #2	$40.85	6.323%	$43.4329	$43.43	$43.45	$43.40
Purchase #3	$142.37	9.761%	$156.2667	$156.27	$156.25	$156.30
Purchase #4	$80.50	4.755%	$84.3278	$84.33	$84.35	$84.30
Purchase #5	$245.64	13.432%	$278.6344	$278.63	$278.65	$278.60
Purchase #6	$106.62	4.454%	$111.3689	$111.37	$111.35	$111.40
Purchase #7	$217.65	9.355%	$238.0112	$238.01	$238.00	$238.00
7 purchase totals =	$927.25		$1,011.9962	$1,011.99	$1,012.00	$1,012.00