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	$133.43	4.429%	$139.3396	$139.34	$139.35	$139.30
Purchase #2	$216.72	4.636%	$226.7671	$226.77	$226.75	$226.80
Purchase #3	$124.49	6.270%	$132.2955	$132.30	$132.30	$132.30
Purchase #4	$116.36	13.384%	$131.9336	$131.93	$131.95	$131.90
Purchase #5	$234.86	4.273%	$244.8956	$244.90	$244.90	$244.90
Purchase #6	$222.33	6.273%	$236.2768	$236.28	$236.30	$236.30
Purchase #7	$56.90	5.206%	$59.8622	$59.86	$59.85	$59.90
7 purchase totals =	$1,105.09		$1,171.3704	$1,171.38	$1,171.40	$1,171.40