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	$70.40	11.127%	$78.2334	$78.23	$78.25	$78.20
Purchase #2	$181.34	7.739%	$195.3739	$195.37	$195.35	$195.40
Purchase #3	$21.75	12.714%	$24.5153	$24.52	$24.50	$24.50
Purchase #4	$24.87	4.690%	$26.0364	$26.04	$26.05	$26.00
Purchase #5	$196.90	8.463%	$213.5636	$213.56	$213.55	$213.60
Purchase #6	$98.43	13.651%	$111.8667	$111.87	$111.85	$111.90
Purchase #7	$221.37	7.685%	$238.3823	$238.38	$238.40	$238.40
7 purchase totals =	$815.06		$887.9716	$887.97	$887.95	$888.00