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	$133.35	3.590%	$138.1373	$138.14	$138.15	$138.10
Purchase #2	$50.40	9.413%	$55.1442	$55.14	$55.15	$55.10
Purchase #3	$246.38	13.498%	$279.6364	$279.64	$279.65	$279.60
Purchase #4	$163.38	5.153%	$171.799	$171.80	$171.80	$171.80
Purchase #5	$81.66	10.131%	$89.933	$89.93	$89.95	$89.90
Purchase #6	$230.94	10.634%	$255.4982	$255.50	$255.50	$255.50
Purchase #7	$24.76	10.432%	$27.343	$27.34	$27.35	$27.30
7 purchase totals =	$930.87		$1,017.4911	$1,017.49	$1,017.55	$1,017.30