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	$249.78	4.668%	$261.4397	$261.44	$261.45	$261.40
Purchase #2	$137.46	3.692%	$142.535	$142.54	$142.55	$142.50
Purchase #3	$17.93	12.516%	$20.1741	$20.17	$20.15	$20.20
Purchase #4	$171.29	5.725%	$181.0964	$181.10	$181.10	$181.10
Purchase #5	$163.74	10.602%	$181.0997	$181.10	$181.10	$181.10
Purchase #6	$129.45	9.320%	$141.5147	$141.51	$141.50	$141.50
Purchase #7	$178.63	6.322%	$189.923	$189.92	$189.90	$189.90
7 purchase totals =	$1,048.28		$1,117.7826	$1,117.78	$1,117.75	$1,117.70