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	$243.37	5.328%	$256.3368	$256.34	$256.35	$256.30
Purchase #2	$39.75	9.243%	$43.4241	$43.42	$43.40	$43.40
Purchase #3	$197.83	12.803%	$223.1582	$223.16	$223.15	$223.20
Purchase #4	$135.66	4.208%	$141.3686	$141.37	$141.35	$141.40
Purchase #5	$147.29	6.383%	$156.6915	$156.69	$156.70	$156.70
Purchase #6	$181.36	8.445%	$196.6759	$196.68	$196.70	$196.70
Purchase #7	$174.95	13.664%	$198.8552	$198.86	$198.85	$198.90
7 purchase totals =	$1,120.21		$1,216.5103	$1,216.52	$1,216.50	$1,216.60