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	$129.61	7.461%	$139.2802	$139.28	$139.30	$139.30
Purchase #2	$36.68	7.860%	$39.563	$39.56	$39.55	$39.60
Purchase #3	$227.83	13.639%	$258.9037	$258.90	$258.90	$258.90
Purchase #4	$96.83	13.121%	$109.5351	$109.54	$109.55	$109.50
Purchase #5	$44.42	9.651%	$48.707	$48.71	$48.70	$48.70
Purchase #6	$239.53	11.189%	$266.331	$266.33	$266.35	$266.30
Purchase #7	$168.95	6.449%	$179.8456	$179.85	$179.85	$179.80
7 purchase totals =	$943.85		$1,042.1656	$1,042.17	$1,042.20	$1,042.10