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	$238.79	11.582%	$266.4467	$266.45	$266.45	$266.40
Purchase #2	$68.34	3.263%	$70.5699	$70.57	$70.55	$70.60
Purchase #3	$203.36	6.620%	$216.8224	$216.82	$216.80	$216.80
Purchase #4	$171.83	6.289%	$182.6364	$182.64	$182.65	$182.60
Purchase #5	$56.80	5.399%	$59.8666	$59.87	$59.85	$59.90
Purchase #6	$86.53	11.688%	$96.6436	$96.64	$96.65	$96.60
Purchase #7	$172.72	12.857%	$194.9266	$194.93	$194.95	$194.90
7 purchase totals =	$998.37		$1,087.9122	$1,087.92	$1,087.90	$1,087.80