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	$123.25	13.399%	$139.7643	$139.76	$139.75	$139.80
Purchase #2	$202.51	5.418%	$213.482	$213.48	$213.50	$213.50
Purchase #3	$149.80	10.513%	$165.5485	$165.55	$165.55	$165.50
Purchase #4	$220.39	13.866%	$250.9493	$250.95	$250.95	$250.90
Purchase #5	$108.48	7.229%	$116.322	$116.32	$116.30	$116.30
Purchase #6	$92.57	12.828%	$104.4449	$104.44	$104.45	$104.40
Purchase #7	$28.91	7.540%	$31.0898	$31.09	$31.10	$31.10
7 purchase totals =	$925.91		$1,021.6008	$1,021.59	$1,021.60	$1,021.50