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	$150.55	12.769%	$169.7737	$169.77	$169.75	$169.80
Purchase #2	$37.90	13.130%	$42.8763	$42.88	$42.90	$42.90
Purchase #3	$132.90	3.309%	$137.2977	$137.30	$137.30	$137.30
Purchase #4	$55.25	3.828%	$57.365	$57.37	$57.35	$57.40
Purchase #5	$225.42	4.334%	$235.1897	$235.19	$235.20	$235.20
Purchase #6	$143.76	12.311%	$161.4583	$161.46	$161.45	$161.50
Purchase #7	$82.68	4.564%	$86.4535	$86.45	$86.45	$86.50
7 purchase totals =	$828.46		$890.4142	$890.42	$890.40	$890.60