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	$27.90	12.635%	$31.4252	$31.43	$31.45	$31.40
Purchase #2	$245.47	9.351%	$268.4239	$268.42	$268.40	$268.40
Purchase #3	$177.59	12.282%	$199.4016	$199.40	$199.40	$199.40
Purchase #4	$187.75	6.173%	$199.3398	$199.34	$199.35	$199.30
Purchase #5	$118.89	13.821%	$135.3218	$135.32	$135.30	$135.30
Purchase #6	$14.45	9.509%	$15.8241	$15.82	$15.80	$15.80
Purchase #7	$54.25	6.613%	$57.8376	$57.84	$57.85	$57.80
7 purchase totals =	$826.30		$907.5740	$907.57	$907.55	$907.40