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	$194.59	12.205%	$218.3397	$218.34	$218.35	$218.30
Purchase #2	$134.34	6.708%	$143.3515	$143.35	$143.35	$143.40
Purchase #3	$37.99	6.782%	$40.5665	$40.57	$40.55	$40.60
Purchase #4	$159.37	12.581%	$179.4203	$179.42	$179.40	$179.40
Purchase #5	$111.39	5.334%	$117.3315	$117.33	$117.35	$117.30
Purchase #6	$38.38	5.240%	$40.3911	$40.39	$40.40	$40.40
Purchase #7	$37.47	6.555%	$39.9262	$39.93	$39.95	$39.90
7 purchase totals =	$713.53		$779.3268	$779.33	$779.35	$779.30