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	$77.88	3.320%	$80.4656	$80.47	$80.45	$80.50
Purchase #2	$102.63	10.164%	$113.0613	$113.06	$113.05	$113.10
Purchase #3	$234.78	12.583%	$264.3224	$264.32	$264.30	$264.30
Purchase #4	$237.72	11.853%	$265.897	$265.90	$265.90	$265.90
Purchase #5	$168.67	6.448%	$179.5458	$179.55	$179.55	$179.50
Purchase #6	$168.92	8.516%	$183.3052	$183.31	$183.30	$183.30
Purchase #7	$87.93	9.330%	$96.1339	$96.13	$96.15	$96.10
7 purchase totals =	$1,078.53		$1,182.7312	$1,182.74	$1,182.70	$1,182.70