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	$134.86	3.395%	$139.4385	$139.44	$139.45	$139.40
Purchase #2	$96.89	3.298%	$100.0854	$100.09	$100.10	$100.10
Purchase #3	$53.66	11.344%	$59.7472	$59.75	$59.75	$59.70
Purchase #4	$114.63	8.377%	$124.2326	$124.23	$124.25	$124.20
Purchase #5	$127.48	3.443%	$131.8691	$131.87	$131.85	$131.90
Purchase #6	$213.78	9.503%	$234.0955	$234.10	$234.10	$234.10
Purchase #7	$61.44	13.693%	$69.853	$69.85	$69.85	$69.90
7 purchase totals =	$802.74		$859.3213	$859.33	$859.35	$859.30