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	$128.33	9.505%	$140.5278	$140.53	$140.55	$140.50
Purchase #2	$55.43	11.499%	$61.8039	$61.80	$61.80	$61.80
Purchase #3	$144.53	11.398%	$161.0035	$161.00	$161.00	$161.00
Purchase #4	$100.94	8.869%	$109.8924	$109.89	$109.90	$109.90
Purchase #5	$51.85	10.685%	$57.3902	$57.39	$57.40	$57.40
Purchase #6	$90.86	13.650%	$103.2624	$103.26	$103.25	$103.30
Purchase #7	$60.36	10.651%	$66.7889	$66.79	$66.80	$66.80
7 purchase totals =	$632.30		$700.6691	$700.66	$700.70	$700.70